feat(entity-dim): 账套维度收口批 — subjects/analysis_results 加列 + 分析结论账套化 + 模板实例化构造点补账套

- ① kpi_templates instantiate 构造点显式传会话账套（原缺 entity_id ⇒ 静默落 e1），kpi_code 判重按账套收紧
- ② kpi_subject_map 3 个读取点加护栏注释（不加列、不改语义）
- ③ subjects 分层：读口 union（NULL=全局标准准则科目 / N=账套私有），UPSERT 唯一键改 (entity_id, subject_code)
- ④ analysis_results 账套化：读/写/删三端点按会话账套判定归属（列未落地时 kpi_code JOIN 止血），
     无归属行进 unattributed 登记、删除一律 404
- 模型层按现网 DDL 补齐：KPIDefinition(template_id/is_system + uk_entity_kpi)、AnalysisResult.entity_id、Subject.entity_id
- 新增 migrate_{subjects,analysis_results}_entity_id_20260923.py（--check/--apply/--down）、
  22 条对账用例 test_entity_dimension_convergence_20260923.py

DDL 已由 ops 受控通道落地（subjects 21:31:56 / analysis_results 21:31:59 CST，审批 1e9b4d9a/5ffb1640）
本提交为切片提交，未 push（发布须另取放行）

backend/app/api/data_classification.py

@@ -107,7 +107,11 @@ def _query_items(
     items: list[dict] = []
 
     if not data_type or data_type == "subject":
-        q = db.query(Subject).filter(Subject.is_active == 1)
+        # 账套分层（2026-09-23）：全局标准准则科目 ∪ 本账套私有明细（与 KPI 侧同一账套口径）
+        q = db.query(Subject).filter(
+            Subject.is_active == 1,
+            (Subject.entity_id.is_(None)) | (Subject.entity_id == entity_id),
+        )
         if data_level:
             q = q.filter(Subject.data_level == data_level)
         if important == 1:
@@ -181,9 +185,13 @@ def get_stats(
     current_user = Depends(require_auth),
 ):
     """数据分类分级统计概览（评估前准备看板）"""
-    subject_total = db.query(Subject).filter(Subject.is_active == 1).count()
+    subject_total = db.query(Subject).filter(
+        Subject.is_active == 1,
+        (Subject.entity_id.is_(None)) | (Subject.entity_id == entity_id),
+    ).count()
     subject_marked = db.query(Subject).filter(
-        Subject.is_active == 1, Subject.important_flag == 1
+        Subject.is_active == 1, Subject.important_flag == 1,
+        (Subject.entity_id.is_(None)) | (Subject.entity_id == entity_id),
     ).count()
     kpi_total = db.query(KPIDefinition).filter(
         KPIDefinition.status == "active", KPIDefinition.entity_id == entity_id