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/design.md

@@ -0,0 +1,134 @@
+## Context
+
+collaboration spec 要求即時通知透過 WebSocket 推播，但現行 NotificationService 僅寫入資料庫，未實作即時推送。
+
+## Goals / Non-Goals
+
+**Goals:**
+- 建立 WebSocket 連線管理基礎設施
+- 通知建立時透過 Redis Pub/Sub 廣播
+- 使用者連線時補送未讀通知
+- 前端即時接收並更新通知
+
+**Non-Goals:**
+- 不實作通知偏好設定（靜音/訂閱）
+- 不實作 Push Notification (PWA/Mobile)
+- 不實作通知分組或摺疊
+
+## Decisions
+
+### 1. WebSocket 連線管理
+
+**Decision:** 使用 in-memory dict + Redis Pub/Sub
+
+**Rationale:**
+- 單 process 內使用 dict 維護 WebSocket 連線
+- 跨 process 透過 Redis Pub/Sub 廣播
+- 簡單且符合現有架構
+
+```python
+class ConnectionManager:
+    def __init__(self):
+        self.active_connections: Dict[str, List[WebSocket]] = {}
+
+    async def connect(self, user_id: str, websocket: WebSocket):
+        await websocket.accept()
+        if user_id not in self.active_connections:
+            self.active_connections[user_id] = []
+        self.active_connections[user_id].append(websocket)
+
+    async def disconnect(self, user_id: str, websocket: WebSocket):
+        self.active_connections[user_id].remove(websocket)
+        if not self.active_connections[user_id]:
+            del self.active_connections[user_id]
+
+    async def send_to_user(self, user_id: str, message: dict):
+        if user_id in self.active_connections:
+            for connection in self.active_connections[user_id]:
+                await connection.send_json(message)
+```
+
+### 2. Redis Pub/Sub 架構
+
+**Decision:** 使用 user-specific channel
+
+**Rationale:**
+- Channel 命名: `notifications:{user_id}`
+- 避免 broadcast 給不相關的 worker
+- 減少訊息處理量
+
+```python
+async def publish_notification(user_id: str, notification: dict):
+    channel = f"notifications:{user_id}"
+    await redis.publish(channel, json.dumps(notification))
+
+async def subscribe_notifications(user_id: str):
+    pubsub = redis.pubsub()
+    await pubsub.subscribe(f"notifications:{user_id}")
+    return pubsub
+```
+
+### 3. 連線時補送未讀
+
+**Decision:** 連線建立後立即查詢並推送
+
+**Rationale:**
+- 確保使用者不漏接通知
+- 簡化前端狀態同步邏輯
+
+```python
+@router.websocket("/ws/notifications")
+async def websocket_endpoint(websocket: WebSocket, token: str = Query(...)):
+    user = await verify_ws_token(token)
+    await manager.connect(user.id, websocket)
+
+    # 連線時補送未讀
+    unread = get_unread_notifications(db, user.id)
+    await websocket.send_json({
+        "type": "unread_sync",
+        "notifications": [n.dict() for n in unread]
+    })
+
+    # 開始監聽
+    await listen_for_notifications(user.id, websocket)
+```
+
+### 4. 訊息格式
+
+**Decision:** 統一 JSON 格式
+
+```json
+{
+  "type": "notification",
+  "data": {
+    "id": "uuid",
+    "type": "mention|assignment|blocker|...",
+    "title": "...",
+    "message": "...",
+    "reference_type": "task|comment",
+    "reference_id": "uuid",
+    "created_at": "ISO8601"
+  }
+}
+```
+
+## API Changes
+
+```
+# 新增 WebSocket endpoint
+WS /ws/notifications?token={jwt_token}
+
+# 訊息類型
+-> {"type": "unread_sync", "notifications": [...]}  # 連線時
+-> {"type": "notification", "data": {...}}          # 新通知
+-> {"type": "mark_read", "notification_id": "..."}  # 已讀確認
+<- {"type": "ping"}                                  # 心跳
+```
+
+## Risks / Trade-offs
+
+| Risk | Mitigation |
+|------|------------|
+| WebSocket 連線數量大 | 使用心跳偵測清理斷線 |
+| Redis Pub/Sub 可靠性 | Pub/Sub 為 fire-and-forget，已有 DB 紀錄作為 fallback |
+| Token 驗證 in query | WebSocket 標準限制，token 有過期機制 |