perf(assignments): 优化分配管理页面加载性能与角标数量展示

- 前端改造为服务端分页查询 (accountApi.listPaged)，避免一次性拉取 1.6 万+ 账号导致页面卡死
- 优化后端 assignments_summary 聚合查询，消除大子查询临时表
- 修复 Badge 默认 99+ 限制，设置 overflowCount 支持展示完整账号数量
- 修复测试用例 test_business_events.py 当前时间跨天断言问题

web/backend/routers/accounts.py

@@ -124,7 +124,7 @@ def _filter_accounts_query(
 ):
     """复用列表筛选条件，供分页列表和全量批量操作保持一致。"""
     if _query_bool(has_cookie):
-        query = query.filter(Account.id.in_(cookie_account_ids_query(db)))
+        query = query.filter(Account.cookie.isnot(None), Account.cookie != "")
     if _query_bool(assigned_only) and user_has_permission(current, "account:view_all"):
         query = query.filter(Account.assigned_to.isnot(None))
     # 归属筛选：未分配 / 已分配，再叠加「指定客服」。与其它条件（标签、CK、
@@ -1009,30 +1009,40 @@ def assignments_summary(
     current: User = Depends(require_permission("account:assign")),
 ):
     """分配概览：每个客服分配了多少账号（仅统计当前仍持有 CK 的账号）。"""
-    cookie_subq = select(Account.id).where(cookie_holding_filter())
-    cookie_accounts = db.query(Account).filter(Account.id.in_(cookie_subq)).subquery()
-
     results = (
-        db.query(
-            User.id, User.username, func.count(cookie_accounts.c.id).label("count")
+        db.query(User.id, User.username, func.count(Account.id).label("count"))
+        .outerjoin(
+            Account,
+            and_(
+                Account.assigned_to == User.id,
+                Account.cookie.isnot(None),
+                Account.cookie != "",
+            ),
         )
-        .outerjoin(cookie_accounts, cookie_accounts.c.assigned_to == User.id)
         .filter(User.role == "support")
         .group_by(User.id, User.username)
-        .order_by(func.count(cookie_accounts.c.id).desc())
+        .order_by(func.count(Account.id).desc())
         .all()
     )
     total_unassigned = (
-        db.query(func.count(cookie_accounts.c.id))
-        .filter(cookie_accounts.c.assigned_to.is_(None))
+        db.query(func.count(Account.id))
+        .filter(
+            Account.assigned_to.is_(None),
+            Account.cookie.isnot(None),
+            Account.cookie != "",
+        )
         .scalar()
     ) or 0
+    total_assigned = sum(int(cnt or 0) for _, _, cnt in results)
+    total_accounts = total_assigned + total_unassigned
     return {
         "support_users": [
-            {"id": uid, "username": uname, "assigned_count": cnt}
+            {"id": uid, "username": uname, "assigned_count": int(cnt or 0)}
             for uid, uname, cnt in results
         ],
         "unassigned_count": total_unassigned,
+        "assigned_count": total_assigned,
+        "total_count": total_accounts,
     }