feat: Add AI-generated commit messages

Integrate Claude Haiku to automatically generate commit messages when
committing worktree changes. Shows a sparkle animation while generating
and auto-populates the commit message field.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

apps/ui/src/lib/http-api-client.ts

@@ -1681,6 +1681,8 @@ export class HttpApiClient implements ElectronAPI {
       }),
     commit: (worktreePath: string, message: string) =>
       this.post('/api/worktree/commit', { worktreePath, message }),
+    generateCommitMessage: (worktreePath: string) =>
+      this.post('/api/worktree/generate-commit-message', { worktreePath }),
     push: (worktreePath: string, force?: boolean) =>
       this.post('/api/worktree/push', { worktreePath, force }),
     createPR: (worktreePath: string, options?: any) =>