feat(m12): meetings + schedule conflict detection, tests, e2e

- MeetingRepository (CRUD, soft-delete, members, findMeetingsByUserInRange
  overlap) + CalendarRepository.findByCreatorInRange + TodoRepository.
  findHighPriorityByAssignee
- MeetingService (createMeeting tx+members, meeting_invited notify,
  meeting_created activity, SSE meeting.created; updateMeeting/updateMinutes/
  deleteMeeting; checkScheduleConflicts = other meetings overlap + calendar
  events overlap + high-priority todos due +-3d, time-overlap logic,
  excludeMeetingId; conflicts are warnings)
- APIs: meetings list/create/edit + /check conflict check
- Screens: meetings page + MeetingForm(member checkboxes, conflict display)
  + ConflictWarning, ProjectNav link
- Unit tests (MeetingRepository, MeetingService incl. conflict algorithm)
  + e2e meetings

repositories/CalendarRepository.ts

@@ -65,6 +65,23 @@ export class CalendarRepository {
     return rows.map(mapEvent);
   }
 
+  /** 指定ユーザーが作成したイベントのうち [from,to] と時間重複するもの(スケジュール重複判定用) */
+  findByCreatorInRange(
+    userId: number,
+    from: string,
+    to: string
+  ): CalendarEvent[] {
+    const rows = this.db.query<CalendarEventRow>(
+      `SELECT * FROM calendar_events
+       WHERE created_by_id = @userId AND deleted_at IS NULL
+         AND end_at IS NOT NULL
+         AND start_at <= @to AND end_at >= @from
+       ORDER BY start_at ASC`,
+      { userId, from, to }
+    );
+    return rows.map(mapEvent);
+  }
+
   findEventById(id: number): CalendarEvent | null {
     const row = this.db.get<CalendarEventRow>(
       'SELECT * FROM calendar_events WHERE id = @id AND deleted_at IS NULL',