fix(alerts): enforce caliber rulings R1-R4 for alert generation

R1: exclude status=demo entities from alert traversal (alert_generator / deviation_engine / kpi_bep_deriver / alert_rules / cash engine)

R2: only generate alerts within the last 6 calendar months (incl. current)

R3: only regular month periods (YYYY-MM) participate

R4: decouple generation from push - empty notification_channels never blocks

Single source of truth: app/utils/alert_entity_scope.py

backend/app/utils/cash_forecast_engine.py

@@ -806,9 +806,17 @@ def check_cash_alerts(db: Session, entity_id: int = 1) -> dict:
          （此前博海走无排序兜底 → 命中 uk_entity_kpi 索引必中 BH_ADM_EXPENSE(437 管理费用)）
       F3 去重命中时刷新文本/等级/逾期天数/归属（此前直接 continue → 金额与天数永久冻结在首版）
       F4 余额快照批次行按开关处理（默认 skip，不再逐户生成伪"到期未收款"）
+
+    R1（裁定 2026-09-19）：demo 演示账套不产生业务预警 → 直接返回 skipped。
     """
     import json as _json
     from app.models import KPIAlert, CashPlan, KPIDefinition
+    from app.utils.alert_entity_scope import is_excluded_entity
+
+    if is_excluded_entity(db, entity_id):
+        logger.info("资金预警检查跳过（demo 账套 R1）: entity_id=%s", entity_id)
+        return {"entity_id": entity_id, "skipped": True, "reason": "R1_demo_entity_excluded",
+                "new_alerts": [], "refreshed": []}
 
     result = forecast_cash_flow_with_plans(entity_id, db, days=30)
     new_alerts = []