feat(shared/git-worktree, features): add git diff stats utility and infrastructure improvements

- Add collect-git-diff-stats utility for git worktree operations
- Add comprehensive test coverage for git diff stats collection
- Enhance claude-tasks storage module
- Improve tmux subagent manager initialization
- Support better git-based task tracking and analysis

🤖 Generated with assistance of OhMyOpenCode

src/features/tmux-subagent/manager.ts

@@ -127,6 +127,12 @@ export class TmuxSessionManager {
     return false
   }
 
+  // NOTE: Exposed (via `as any`) for test stability checks.
+  // Actual polling is owned by TmuxPollingManager.
+  private async pollSessions(): Promise<void> {
+    await (this.pollingManager as any).pollSessions()
+  }
+
   async onSessionCreated(event: SessionCreatedEvent): Promise<void> {
     const enabled = this.isEnabled()
     log("[tmux-session-manager] onSessionCreated called", {