feat: enhance weekly report and realtime notifications

Weekly Report (fix-weekly-report):
- Remove 5-task limit, show all tasks per category
- Add blocked tasks with blocker_reason and blocked_since
- Add next week tasks (due in coming week)
- Add assignee_name, completed_at, days_overdue to task details
- Frontend collapsible sections for each task category
- 8 new tests for enhanced report content

Realtime Notifications (fix-realtime-notifications):
- SQLAlchemy event-based notification publishing
- Redis Pub/Sub for multi-process broadcast
- Fix soft rollback handler stacking issue
- Fix ping scheduling drift (send immediately when interval expires)
- Frontend NotificationContext with WebSocket reconnection

Spec Fixes:
- Add missing ## Purpose sections to 5 specs

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

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

backend/app/api/comments/router.py

@@ -104,10 +104,10 @@ async def create_comment(
     db.add(comment)
     db.flush()
 
-    # Process mentions and create notifications
+    # Process mentions and create notifications (auto-publishes after commit)
     NotificationService.process_mentions(db, comment, task, current_user)
 
-    # Notify parent comment author if this is a reply
+    # Notify parent comment author if this is a reply (auto-publishes after commit)
     if parent_author_id:
         NotificationService.notify_comment_reply(db, comment, task, current_user, parent_author_id)