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>

openspec/changes/archive/2025-12-30-fix-realtime-notifications/proposal.md

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+# Change: Fix Real-time Notifications Alignment
+
+## Why
+現行實作與 collaboration spec 的 Real-time Notifications requirement 有以下差距：
+1. 通知僅寫入資料庫，未透過 WebSocket 即時推播
+2. 未使用 Redis Pub/Sub 處理多 process 推播
+3. 使用者連線時未補送未讀通知
+
+## What Changes
+- **WebSocket Manager** - 建立 WebSocket 連線管理模組
+- **Redis Pub/Sub** - 整合 Redis 處理跨 process 通知推播
+- **NotificationService** - 新增即時推播呼叫
+- **API** - 新增 `/ws/notifications` WebSocket endpoint
+- **Frontend** - 整合 WebSocket 接收即時通知
+
+## Impact
+- Affected specs: `collaboration`
+- Affected code:
+  - `backend/app/core/websocket.py` - 新增 WebSocket 管理
+  - `backend/app/core/redis_pubsub.py` - 新增 Redis Pub/Sub 服務
+  - `backend/app/services/notification_service.py` - 加入即時推播
+  - `backend/app/api/notifications/router.py` - 新增 WebSocket endpoint
+  - `frontend/src/services/websocket.ts` - 新增 WebSocket client
+  - `frontend/src/contexts/NotificationContext.tsx` - 整合即時通知
+
+## Implementation Phases
+
+### Phase 1: WebSocket Infrastructure
+- WebSocket 連線管理器
+- 使用者連線/斷線處理
+- 連線時補送未讀通知
+
+### Phase 2: Redis Pub/Sub Integration
+- Redis Pub/Sub 服務封裝
+- 多 process 通知廣播
+- 訊息序列化/反序列化
+
+### Phase 3: Service Integration
+- NotificationService 加入推播
+- 前端 WebSocket client
+- 未讀數量即時更新
+
+## Dependencies
+- collaboration (已完成)
+- Redis 已在 user-auth 中使用
+
+## Technical Decisions
+- 使用 FastAPI WebSocket 原生支援
+- Redis Pub/Sub 處理多 worker 同步
+- 使用者以 user_id 為 channel key