feat: 实现月度记账开始日期功能

- 添加 Settings 实体和 DAO 来持久化存储设置
- 创建 SettingsRepository 管理设置数据
- 添加数据库迁移从版本 4 到版本 5
- 在设置界面添加月度开始日期选择器（1-28号）
- 创建 DateUtils 工具类处理基于月度开始日期的日期计算
- 更新 HomeViewModel 和 AnalysisViewModel 使用月度开始日期进行统计
- 修复日期选择器中数字显示不完整的问题

app/src/main/java/com/yovinchen/bookkeeping/data/BudgetDao.kt

@@ -0,0 +1,105 @@
+package com.yovinchen.bookkeeping.data
+
+import androidx.room.*
+import com.yovinchen.bookkeeping.model.Budget
+import com.yovinchen.bookkeeping.model.BudgetType
+import kotlinx.coroutines.flow.Flow
+import java.util.Date
+
+/**
+ * 预算数据访问对象
+ * 提供预算相关的数据库操作接口
+ */
+@Dao
+interface BudgetDao {
+    
+    /**
+     * 插入新预算
+     */
+    @Insert
+    suspend fun insertBudget(budget: Budget): Long
+    
+    /**
+     * 更新预算
+     */
+    @Update
+    suspend fun updateBudget(budget: Budget)
+    
+    /**
+     * 删除预算
+     */
+    @Delete
+    suspend fun deleteBudget(budget: Budget)
+    
+    /**
+     * 根据ID获取预算
+     */
+    @Query("SELECT * FROM budgets WHERE id = :budgetId")
+    suspend fun getBudgetById(budgetId: Int): Budget?
+    
+    /**
+     * 获取所有启用的预算
+     */
+    @Query("SELECT * FROM budgets WHERE isEnabled = 1 ORDER BY type, amount DESC")
+    fun getAllEnabledBudgets(): Flow<List<Budget>>
+    
+    /**
+     * 获取所有预算（包括禁用的）
+     */
+    @Query("SELECT * FROM budgets ORDER BY type, amount DESC")
+    fun getAllBudgets(): Flow<List<Budget>>
+    
+    /**
+     * 根据类型获取预算
+     */
+    @Query("SELECT * FROM budgets WHERE type = :type AND isEnabled = 1")
+    fun getBudgetsByType(type: BudgetType): Flow<List<Budget>>
+    
+    /**
+     * 获取总预算
+     */
+    @Query("SELECT * FROM budgets WHERE type = 'TOTAL' AND isEnabled = 1 AND :date BETWEEN startDate AND endDate LIMIT 1")
+    suspend fun getTotalBudget(date: Date): Budget?
+    
+    /**
+     * 获取指定分类的预算
+     */
+    @Query("SELECT * FROM budgets WHERE type = 'CATEGORY' AND categoryName = :categoryName AND isEnabled = 1 AND :date BETWEEN startDate AND endDate LIMIT 1")
+    suspend fun getCategoryBudget(categoryName: String, date: Date): Budget?
+    
+    /**
+     * 获取指定成员的预算
+     */
+    @Query("SELECT * FROM budgets WHERE type = 'MEMBER' AND memberId = :memberId AND isEnabled = 1 AND :date BETWEEN startDate AND endDate LIMIT 1")
+    suspend fun getMemberBudget(memberId: Int, date: Date): Budget?
+    
+    /**
+     * 获取当前有效的所有预算
+     */
+    @Query("SELECT * FROM budgets WHERE isEnabled = 1 AND :date BETWEEN startDate AND endDate ORDER BY type, amount DESC")
+    fun getActiveBudgets(date: Date): Flow<List<Budget>>
+    
+    /**
+     * 更新预算的启用状态
+     */
+    @Query("UPDATE budgets SET isEnabled = :enabled, updatedAt = :updatedAt WHERE id = :budgetId")
+    suspend fun updateBudgetEnabled(budgetId: Int, enabled: Boolean, updatedAt: Date = Date())
+    
+    /**
+     * 删除所有过期的预算（可选）
+     */
+    @Query("DELETE FROM budgets WHERE endDate < :date AND isEnabled = 0")
+    suspend fun deleteExpiredBudgets(date: Date)
+    
+    /**
+     * 获取指定日期范围内的分类预算
+     */
+    @Query("SELECT * FROM budgets WHERE type = 'CATEGORY' AND isEnabled = 1 AND :date BETWEEN startDate AND endDate")
+    fun getCategoryBudgetsForDate(date: Date): Flow<List<Budget>>
+    
+    /**
+     * 获取指定日期范围内的成员预算
+     */
+    @Query("SELECT * FROM budgets WHERE type = 'MEMBER' AND isEnabled = 1 AND :date BETWEEN startDate AND endDate")
+    fun getMemberBudgetsForDate(date: Date): Flow<List<Budget>>
+}

app/src/main/java/com/yovinchen/bookkeeping/data/BudgetRepository.kt

@@ -0,0 +1,215 @@
+package com.yovinchen.bookkeeping.data
+
+import com.yovinchen.bookkeeping.model.*
+import kotlinx.coroutines.flow.Flow
+import kotlinx.coroutines.flow.combine
+import kotlinx.coroutines.flow.first
+import kotlinx.coroutines.flow.map
+import java.util.Date
+import javax.inject.Inject
+import javax.inject.Singleton
+
+/**
+ * 预算仓库类
+ * 提供预算相关的业务逻辑和数据访问
+ */
+class BudgetRepository(
+    private val budgetDao: BudgetDao,
+    private val bookkeepingDao: BookkeepingDao,
+    private val memberDao: MemberDao
+) {
+    
+    /**
+     * 创建新预算
+     */
+    suspend fun createBudget(budget: Budget): Long {
+        return budgetDao.insertBudget(budget)
+    }
+    
+    /**
+     * 更新预算
+     */
+    suspend fun updateBudget(budget: Budget) {
+        budgetDao.updateBudget(budget.copy(updatedAt = Date()))
+    }
+    
+    /**
+     * 删除预算
+     */
+    suspend fun deleteBudget(budget: Budget) {
+        budgetDao.deleteBudget(budget)
+    }
+    
+    /**
+     * 获取所有预算
+     */
+    fun getAllBudgets(): Flow<List<Budget>> {
+        return budgetDao.getAllBudgets()
+    }
+    
+    /**
+     * 获取所有启用的预算
+     */
+    fun getAllEnabledBudgets(): Flow<List<Budget>> {
+        return budgetDao.getAllEnabledBudgets()
+    }
+    
+    /**
+     * 获取当前有效的预算状态
+     */
+    fun getActiveBudgetStatuses(date: Date = Date()): Flow<List<BudgetStatus>> {
+        return combine(
+            budgetDao.getActiveBudgets(date),
+            bookkeepingDao.getAllRecords(),
+            memberDao.getAllMembers()
+        ) { budgets, records, members ->
+            budgets.map { budget ->
+                val spent = calculateSpent(budget, records, members, date)
+                val remaining = budget.amount - spent
+                val percentage = if (budget.amount > 0) spent / budget.amount else 0.0
+                
+                BudgetStatus(
+                    budget = budget,
+                    spent = spent,
+                    remaining = remaining,
+                    percentage = percentage,
+                    isOverBudget = spent > budget.amount,
+                    isNearLimit = percentage >= budget.alertThreshold
+                )
+            }
+        }
+    }
+    
+    /**
+     * 计算预算已花费金额
+     */
+    private fun calculateSpent(
+        budget: Budget,
+        records: List<BookkeepingRecord>,
+        members: List<Member>,
+        currentDate: Date
+    ): Double {
+        // 只计算支出类型的记录
+        val expenseRecords = records.filter { 
+            it.type == TransactionType.EXPENSE &&
+            it.date >= budget.startDate &&
+            it.date <= budget.endDate &&
+            it.date <= currentDate
+        }
+        
+        return when (budget.type) {
+            BudgetType.TOTAL -> {
+                // 总预算：计算所有支出
+                expenseRecords.sumOf { it.amount }
+            }
+            BudgetType.CATEGORY -> {
+                // 分类预算：计算指定分类的支出
+                expenseRecords
+                    .filter { it.category == budget.categoryName }
+                    .sumOf { it.amount }
+            }
+            BudgetType.MEMBER -> {
+                // 成员预算：计算指定成员的支出
+                expenseRecords
+                    .filter { it.memberId == budget.memberId }
+                    .sumOf { it.amount }
+            }
+        }
+    }
+    
+    /**
+     * 获取总预算状态
+     */
+    suspend fun getTotalBudgetStatus(date: Date = Date()): BudgetStatus? {
+        val budget = budgetDao.getTotalBudget(date) ?: return null
+        val records = bookkeepingDao.getAllRecords().first()
+        val members = memberDao.getAllMembers().first()
+        
+        val spent = calculateSpent(budget, records, members, date)
+        val remaining = budget.amount - spent
+        val percentage = if (budget.amount > 0) spent / budget.amount else 0.0
+        
+        return BudgetStatus(
+            budget = budget,
+            spent = spent,
+            remaining = remaining,
+            percentage = percentage,
+            isOverBudget = spent > budget.amount,
+            isNearLimit = percentage >= budget.alertThreshold
+        )
+    }
+    
+    /**
+     * 获取分类预算状态
+     */
+    fun getCategoryBudgetStatuses(date: Date = Date()): Flow<List<BudgetStatus>> {
+        return combine(
+            budgetDao.getCategoryBudgetsForDate(date),
+            bookkeepingDao.getAllRecords(),
+            memberDao.getAllMembers()
+        ) { budgets, records, members ->
+            budgets.map { budget ->
+                val spent = calculateSpent(budget, records, members, date)
+                val remaining = budget.amount - spent
+                val percentage = if (budget.amount > 0) spent / budget.amount else 0.0
+                
+                BudgetStatus(
+                    budget = budget,
+                    spent = spent,
+                    remaining = remaining,
+                    percentage = percentage,
+                    isOverBudget = spent > budget.amount,
+                    isNearLimit = percentage >= budget.alertThreshold
+                )
+            }
+        }
+    }
+    
+    /**
+     * 获取成员预算状态
+     */
+    fun getMemberBudgetStatuses(date: Date = Date()): Flow<List<BudgetStatus>> {
+        return combine(
+            budgetDao.getMemberBudgetsForDate(date),
+            bookkeepingDao.getAllRecords(),
+            memberDao.getAllMembers()
+        ) { budgets, records, members ->
+            budgets.map { budget ->
+                val spent = calculateSpent(budget, records, members, date)
+                val remaining = budget.amount - spent
+                val percentage = if (budget.amount > 0) spent / budget.amount else 0.0
+                
+                BudgetStatus(
+                    budget = budget,
+                    spent = spent,
+                    remaining = remaining,
+                    percentage = percentage,
+                    isOverBudget = spent > budget.amount,
+                    isNearLimit = percentage >= budget.alertThreshold
+                )
+            }
+        }
+    }
+    
+    /**
+     * 检查是否有预算超支或接近限制
+     */
+    suspend fun checkBudgetAlerts(date: Date = Date()): List<BudgetStatus> {
+        val allStatuses = getActiveBudgetStatuses(date).first()
+        return allStatuses.filter { it.isOverBudget || it.isNearLimit }
+    }
+    
+    /**
+     * 更新预算启用状态
+     */
+    suspend fun updateBudgetEnabled(budgetId: Int, enabled: Boolean) {
+        budgetDao.updateBudgetEnabled(budgetId, enabled)
+    }
+    
+    /**
+     * 清理过期的禁用预算
+     */
+    suspend fun cleanupExpiredBudgets() {
+        budgetDao.deleteExpiredBudgets(Date())
+    }
+}

app/src/main/java/com/yovinchen/bookkeeping/model/Budget.kt

@@ -0,0 +1,86 @@
+package com.yovinchen.bookkeeping.model
+
+import androidx.room.Entity
+import androidx.room.PrimaryKey
+import java.util.Date
+
+/**
+ * 预算实体类
+ * 用于设置和跟踪月度预算、分类预算和成员预算
+ */
+@Entity(tableName = "budgets")
+data class Budget(
+    @PrimaryKey(autoGenerate = true)
+    val id: Int = 0,
+    
+    /**
+     * 预算类型：TOTAL（总预算）, CATEGORY（分类预算）, MEMBER（成员预算）
+     */
+    val type: BudgetType,
+    
+    /**
+     * 预算关联的分类名称（仅在 type 为 CATEGORY 时使用）
+     */
+    val categoryName: String? = null,
+    
+    /**
+     * 预算关联的成员ID（仅在 type 为 MEMBER 时使用）
+     */
+    val memberId: Int? = null,
+    
+    /**
+     * 预算金额
+     */
+    val amount: Double,
+    
+    /**
+     * 预算生效开始日期
+     */
+    val startDate: Date,
+    
+    /**
+     * 预算生效结束日期
+     */
+    val endDate: Date,
+    
+    /**
+     * 是否启用此预算
+     */
+    val isEnabled: Boolean = true,
+    
+    /**
+     * 提醒阈值（百分比，如 0.8 表示达到 80% 时提醒）
+     */
+    val alertThreshold: Double = 0.8,
+    
+    /**
+     * 创建时间
+     */
+    val createdAt: Date = Date(),
+    
+    /**
+     * 更新时间
+     */
+    val updatedAt: Date = Date()
+)
+
+/**
+ * 预算类型枚举
+ */
+enum class BudgetType {
+    TOTAL,      // 总预算
+    CATEGORY,   // 分类预算
+    MEMBER      // 成员预算
+}
+
+/**
+ * 预算状态数据类，用于展示预算使用情况
+ */
+data class BudgetStatus(
+    val budget: Budget,
+    val spent: Double,          // 已花费金额
+    val remaining: Double,      // 剩余金额
+    val percentage: Double,     // 使用百分比
+    val isOverBudget: Boolean,  // 是否超预算
+    val isNearLimit: Boolean    // 是否接近预算限制
+)