fix(integrations): 「接收中」跨进程一致，不再跟着 gunicorn 进程抖动

上一版用 `manager.polling()` 判"有没有人在收消息"，那是进程内状态：请求落到持有者
回答 true、落到备用进程回答 false，页面上就会每两秒闪一次"已停止"。

改成查数据库里的 advisory lock（`pg_locks`，objsubid=2 的两段式锁），谁抢到租约所有
进程都看得见。`lease_held()` 自己开一条短会话查，不复用请求会话——接口里常在
`await session.commit()` 之后才拼返回值，那时原事务已经关了。

backend/app/api/integrations.py

@@ -33,7 +33,7 @@ from ..errors import AppError, ErrorCode
 from ..models_integrations import BotChannel, BotMessage
 from ..schemas import ok
 from ..services import wechat_ilink
-from ..services.wechat_bot import manager
+from ..services.wechat_bot import lease_held, manager
 from ..stores import get_store
 
 admin_router = APIRouter(prefix="/workspaces", tags=["外部接入"])
@@ -59,15 +59,15 @@ def render_qr_svg(payload: str) -> str:
     return f"data:image/svg+xml;base64,{encoded}"
 
 
-def _channel_out(channel: BotChannel) -> dict[str, Any]:
+async def _channel_out(channel: BotChannel) -> dict[str, Any]:
     return {
         "id": str(channel.id),
         "kind": channel.kind,
         "name": channel.name,
         "status": channel.status,
         "connected": bool(channel.bot_token_enc) and channel.status == "active",
-        # 只有抢到租约、真在拉消息的进程才算"接收中"；备用进程的任务在等键，不算。
-        "polling": manager.polling(channel.id),
+        # 数据库级租约：谁在真收消息所有进程都认，页面不会跟着进程抖动。
+        "polling": await lease_held(channel.id),
         "ilink_user_id": channel.ilink_user_id,
         "last_seen_at": channel.last_seen_at,
         "last_error": channel.last_error,
@@ -91,7 +91,7 @@ async def list_integrations(ws_id: uuid.UUID, ctx: AdminDep, session: SessionDep
         .where(BotChannel.workspace_id == ws_id)
         .order_by(BotChannel.created_at.desc())
     )
-    return ok({"items": [_channel_out(c) for c in rows.scalars().all()]})
+    return ok({"items": [await _channel_out(c) for c in rows.scalars().all()]})
 
 
 @admin_router.post("/{ws_id}/integrations/wechat/qr")
@@ -168,7 +168,7 @@ async def poll_wechat_login(ws_id: uuid.UUID, qrcode_id: str, ctx: AdminDep, ses
     await get_store().delete(_qr_key(ws_id))
 
     await manager.start(channel.id)
-    return ok({"status": "confirmed", "channel": _channel_out(channel)})
+    return ok({"status": "confirmed", "channel": await _channel_out(channel)})
 
 
 @admin_router.patch("/{ws_id}/integrations/{channel_id}")
@@ -193,7 +193,7 @@ async def update_integration(
         await manager.start(channel.id)
     else:
         await manager.stop(channel.id)
-    return ok({"channel": _channel_out(channel)})
+    return ok({"channel": await _channel_out(channel)})
 
 
 @admin_router.delete("/{ws_id}/integrations/{channel_id}")
@@ -211,7 +211,7 @@ async def disconnect_integration(
     channel.status = "pending"
     channel.last_error = None
     await session.commit()
-    return ok({"channel": _channel_out(channel)})
+    return ok({"channel": await _channel_out(channel)})
 
 
 @admin_router.get("/{ws_id}/integrations/{channel_id}/messages")