feat(project): 댓글 있는 업무에 말풍선 아이콘 표시(달력·타임라인·보드·리스트)

- list_tasks/get_task 에 comment_count 서브쿼리 추가
- 달력 막대/타임라인 항목/보드 카드/리스트 업무열에 댓글 수 말풍선
- 댓글 로드 시 메모리 카운트 동기화

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

app/modules/project/db.py

@@ -297,7 +297,8 @@ class ProjectStore:
         with self._pool.connection() as conn:
             rows = conn.execute(
                 f"SELECT t.*, p.name AS project_name, p.color AS project_color, "
-                f"       s.name AS stage_name, s.is_done_stage "
+                f"       s.name AS stage_name, s.is_done_stage, "
+                f"       (SELECT COUNT(*) FROM task_comments c WHERE c.task_id = t.id) AS comment_count "
                 f"FROM tasks t "
                 f"JOIN projects p ON p.id = t.project_id "
                 f"LEFT JOIN project_stages s ON s.id = t.stage_id "
@@ -311,7 +312,8 @@ class ProjectStore:
         with self._pool.connection() as conn:
             row = conn.execute(
                 "SELECT t.*, p.name AS project_name, p.color AS project_color, "
-                "       s.name AS stage_name, s.is_done_stage "
+                "       s.name AS stage_name, s.is_done_stage, "
+                "       (SELECT COUNT(*) FROM task_comments c WHERE c.task_id = t.id) AS comment_count "
                 "FROM tasks t JOIN projects p ON p.id = t.project_id "
                 "LEFT JOIN project_stages s ON s.id = t.stage_id "
                 "WHERE t.id = %s",