fix(fetch-caliber): 取数层排除半年/预测伪期间 + subjects 响应补 entity_id

R3 期间口径（仅 YYYY-MM）延伸到取数层：新增 alert_entity_scope.month_period_clause()（跨库可移植 SQL 等价式），应用到 15 个文件 26 处「按 period 倒序取最新值/最近N期」位点；dashboard 原 MySQL-only REGEXP 正则收口到同单一事实源。

GET /api/cma/subjects 响应增补 entity_id（NULL=全局标准准则科目 / N=账套私有明细），既有 10 字段语义与名称不变。

证据：pending-tasks/_reports/yanxue-20260924-cma-fetch-caliber-fixes-fullstack.md（改前/改后 A/B：F_NET_PROFIT 2026-H2/-55.0 → 2026-08/-10.46）。新增 7 例回归测试；全量 1 failed(预存在) 1473 passed，基线同项。

backend/app/services/knowledge_service.py

@@ -20,6 +20,7 @@ from sqlalchemy.orm import Session
 from sqlalchemy import func, and_
 
 from app.models import KnowledgeEvent, KnowledgeSummary, OperationLog, KPIAlert, KPIDefinition, KPIValue, UserEntity
+from app.utils.alert_entity_scope import month_period_clause
 
 logger = logging.getLogger("cma.knowledge")
 
@@ -165,7 +166,7 @@ async def _kpi_snapshot(db: Session, entity_id: int = 1) -> list[dict]:
     for k in kpis:
         latest = (
             db.query(KPIValue)
-            .filter(KPIValue.kpi_id == k.id)
+            .filter(KPIValue.kpi_id == k.id, month_period_clause(KPIValue.period))
             .order_by(KPIValue.period.desc())
             .first()
         )