fix: resolve TypeScript and Rust build errors and warnings

- Fixed TypeScript errors in ClaudeCodeSession.tsx:
  - Removed unused imports (Square, PreviewPromptDialog, etc.)
  - Removed unused handleOpenPreview function
  - Fixed unused detectedUrl state variable
- Fixed TypeScript error in StreamMessage.tsx:
  - Removed unused useMemo import
- Fixed TypeScript errors in ToolWidgets.tsx:
  - Prefixed unused result props with underscore in multiple widgets
- Fixed Rust warnings:
  - Removed unused imports in commands modules
  - Prefixed unused variables with underscore
  - Added #[allow(dead_code)] for API methods intended for future use

Closes #31
Closes #23
Closes #21
Closes #22

src-tauri/src/checkpoint/mod.rs

@@ -244,11 +244,13 @@ impl CheckpointPaths {
         self.checkpoint_dir(checkpoint_id).join("messages.jsonl")
     }
     
+    #[allow(dead_code)]
     pub fn file_snapshot_path(&self, _checkpoint_id: &str, file_hash: &str) -> PathBuf {
         // In content-addressable storage, files are stored by hash in the content pool
         self.files_dir.join("content_pool").join(file_hash)
     }
     
+    #[allow(dead_code)]
     pub fn file_reference_path(&self, checkpoint_id: &str, safe_filename: &str) -> PathBuf {
         // References are stored per checkpoint
         self.files_dir.join("refs").join(checkpoint_id).join(format!("{}.json", safe_filename))