fix(cma): entity isolation batch4 (cash plan writes, budget ownership, read leaks, okr template)

P0-A cash.py: scope api_update_plan / api_delete_plan / api_complete_plan /
api_register_payment to session entity (cross-entity id -> 404, aligning with
the file's existing get_entity_id endpoints).
P0-B budget.py: write entity_id on BudgetPlan creation + require the KPI to
belong to the session entity; scope /comparison, /comparison/kpi/{id} and
/deviation-report reads to the session entity.
P1 notifications.py: explicit field whitelist (name/config/enabled) on
update_channel to close mass-assignment.
P1 read leaks scoped to session entity: bot_kpis list, data_quality check/stats
(KPI calibre only; quality-log table has no entity_id column), kpis causality
chain + associate-map (KPI and map ownership), dashboard my-kpis,
customer_dashboard list, kpi_governance audit, budget_generate candidates,
driver_budget history (+ entity_id on its write path), expenses stats
(+ entity_id on its write path).
P2 okr_templates.py: write entity_id on the StrategicMap created by apply.

tests: tests/test_cross_entity_isolation_batch4_20260921.py (30 cases;
RED before fix = 22 failed, GREEN after = 30 passed; full suite 1302 passed /
1 xfailed / 0 failed).

backend/app/api/notifications.py

@@ -52,8 +52,10 @@ def update_channel(ch_id: int, data: dict, db: Session = Depends(get_db)):
     ch = db.query(NotificationChannel).filter(NotificationChannel.id == ch_id).first()
     if not ch:
         raise HTTPException(404, "渠道不存在")
+    # 字段白名单（2026-09-21 mass-assignment 收口）：仅业务字段，其余键忽略
+    _updatable = ("name", "config", "enabled")
     for k, v in data.items():
-        if hasattr(ch, k) and k not in ("id", "created_at"):
+        if k in _updatable:
             setattr(ch, k, v)
     db.commit()
     db.refresh(ch)