feat: implement custom slash commands system

Adds a comprehensive slash command system that allows users to create and manage custom commands:

- Backend implementation in Rust for discovering, loading, and managing slash commands
- Support for both user-level (~/.claude/commands/) and project-level (.claude/commands/) commands
- YAML frontmatter support for command metadata (description, allowed-tools)
- Command namespacing with directory structure (e.g., /namespace:command)
- Detection of special features: bash commands (\!), file references (@), and arguments ($ARGUMENTS)

Frontend enhancements:
- SlashCommandPicker component with autocomplete UI and keyboard navigation
- SlashCommandsManager component for CRUD operations on commands
- Integration with FloatingPromptInput to trigger picker on "/" input
- Visual indicators for command features (bash, files, arguments)
- Grouped display by namespace with search functionality

API additions:
- slash_commands_list: Discover all available commands
- slash_command_get: Retrieve specific command by ID
- slash_command_save: Create or update commands
- slash_command_delete: Remove commands

This implementation provides a foundation for users to create reusable command templates and workflows. Commands are stored as markdown files with optional YAML frontmatter for metadata.

Addresses #127 and #134

src/lib/api.ts

@@ -383,6 +383,36 @@ export interface MCPServerConfig {
   env: Record<string, string>;
 }
 
+/**
+ * Represents a custom slash command
+ */
+export interface SlashCommand {
+  /** Unique identifier for the command */
+  id: string;
+  /** Command name (without prefix) */
+  name: string;
+  /** Full command with prefix (e.g., "/project:optimize") */
+  full_command: string;
+  /** Command scope: "project" or "user" */
+  scope: string;
+  /** Optional namespace (e.g., "frontend" in "/project:frontend:component") */
+  namespace?: string;
+  /** Path to the markdown file */
+  file_path: string;
+  /** Command content (markdown body) */
+  content: string;
+  /** Optional description from frontmatter */
+  description?: string;
+  /** Allowed tools from frontmatter */
+  allowed_tools: string[];
+  /** Whether the command has bash commands (!) */
+  has_bash_commands: boolean;
+  /** Whether the command has file references (@) */
+  has_file_references: boolean;
+  /** Whether the command uses $ARGUMENTS placeholder */
+  accepts_arguments: boolean;
+}
+
 /**
  * Result of adding a server
  */
@@ -1724,5 +1754,85 @@ export const api = {
       console.error("Failed to get merged hooks config:", error);
       throw error;
     }
+  },
+
+  // Slash Commands API methods
+
+  /**
+   * Lists all available slash commands
+   * @param projectPath - Optional project path to include project-specific commands
+   * @returns Promise resolving to array of slash commands
+   */
+  async slashCommandsList(projectPath?: string): Promise<SlashCommand[]> {
+    try {
+      return await invoke<SlashCommand[]>("slash_commands_list", { projectPath });
+    } catch (error) {
+      console.error("Failed to list slash commands:", error);
+      throw error;
+    }
+  },
+
+  /**
+   * Gets a single slash command by ID
+   * @param commandId - Unique identifier of the command
+   * @returns Promise resolving to the slash command
+   */
+  async slashCommandGet(commandId: string): Promise<SlashCommand> {
+    try {
+      return await invoke<SlashCommand>("slash_command_get", { commandId });
+    } catch (error) {
+      console.error("Failed to get slash command:", error);
+      throw error;
+    }
+  },
+
+  /**
+   * Creates or updates a slash command
+   * @param scope - Command scope: "project" or "user"
+   * @param name - Command name (without prefix)
+   * @param namespace - Optional namespace for organization
+   * @param content - Markdown content of the command
+   * @param description - Optional description
+   * @param allowedTools - List of allowed tools for this command
+   * @param projectPath - Required for project scope commands
+   * @returns Promise resolving to the saved command
+   */
+  async slashCommandSave(
+    scope: string,
+    name: string,
+    namespace: string | undefined,
+    content: string,
+    description: string | undefined,
+    allowedTools: string[],
+    projectPath?: string
+  ): Promise<SlashCommand> {
+    try {
+      return await invoke<SlashCommand>("slash_command_save", {
+        scope,
+        name,
+        namespace,
+        content,
+        description,
+        allowedTools,
+        projectPath
+      });
+    } catch (error) {
+      console.error("Failed to save slash command:", error);
+      throw error;
+    }
+  },
+
+  /**
+   * Deletes a slash command
+   * @param commandId - Unique identifier of the command to delete
+   * @returns Promise resolving to deletion message
+   */
+  async slashCommandDelete(commandId: string): Promise<string> {
+    try {
+      return await invoke<string>("slash_command_delete", { commandId });
+    } catch (error) {
+      console.error("Failed to delete slash command:", error);
+      throw error;
+    }
   }
 };