feat(git): add rebase workflow with UI state handling

This introduces Git rebase commands (start, continue, abort) and
exposes whether a rebase is currently in progress via the status
payload. The UI now blocks committing during an active rebase and
shows a dedicated rebase notice with continue/abort actions.

- Add tauri commands for rebase operations and status detection
- Update frontend to render rebase state and controls
- Adjust conflict/resolution messaging and related UI styling

src/lib/types.ts

@@ -41,6 +41,7 @@ export interface GitStatus {
   behind: number;
   files: GitFileStatus[];
   clean: boolean;
+  rebase_in_progress: boolean;
 }
 
 export interface GitFileStatus {