feat(agent-office): notification broadcast + telegram tracking + activity feed API

- Add WebSocket notification messages for task_assigned/task_completed
- Structure telegram send_message return value with ok/message_id
- Track telegram delivery status in task result_data
- Add test_telegram command to stock agent
- Add GET /api/agent-office/activity unified feed endpoint

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

agent-office/app/telegram_bot.py

@@ -26,7 +26,11 @@ async def send_message(text: str, reply_markup: dict = None) -> dict:
     }
     if reply_markup:
         payload["reply_markup"] = reply_markup
-    return await _api("sendMessage", payload)
+    result = await _api("sendMessage", payload)
+    return {
+        "ok": result.get("ok", False),
+        "message_id": result.get("result", {}).get("message_id") if result.get("ok") else None,
+    }
 
 async def send_stock_summary(summary: str) -> dict:
     return await send_message(summary)