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/services/report_reclass.py

@@ -652,7 +652,8 @@ def unmapped_subjects(db, entity_id: int, period: str, basis: str, items: Dict[s
         else:
             q = q.filter(VoucherDetail.period == period)
         rows = apply_voucher_guard(db, q, VoucherDetail).group_by(VoucherDetail.subject_code).all()
-        cats = {c: cat for c, cat in db.query(Subject.subject_code, Subject.category).all()}
+        cats = {c: cat for c, cat in db.query(Subject.subject_code, Subject.category)
+                .filter((Subject.entity_id.is_(None)) | (Subject.entity_id == entity_id)).all()}
     except Exception:  # noqa: BLE001
         return []