feat(knowledge): 企业记忆分区——知识三表entity_id多租户隔离 (entity-memory-partition P1)

- knowledge_events/knowledge_summaries: entity_id NOT NULL DEFAULT 1 + 索引（企业记忆抽屉）
- knowledge_articles: entity_id 可空——NULL=全局共享(CMA教学知识), 有值=企业专属
- knowledge_service 全链路 entity_id: extract_events(KPIAlert直过滤+OperationLog经user_entities归属)/_kpi_snapshot(修跨企业KPI泄漏)/generate_summary/get_last_summary/run_*/sync
- api/knowledge.py 8端点 Depends(get_entity_id) 强制过滤；详情越权404
- api/knowledge_articles.py 全局∪本企业查询；企业专属越权404
- 生产DB三表ALTER+索引已完成; 存量38篇教学文章保持NULL全局共享
- 测试 test_security_knowledge_partition.py 8条(双实体互查越权/生成自动带entity/全局文章双可见)
- 方案文档 docs/knowledge-entity-partition-plan-20260903.md（附评审决策点）

backend/app/models/knowledge.py

@@ -22,6 +22,7 @@ class KnowledgeEvent(Base):
     __tablename__ = "knowledge_events"
 
     id = Column(Integer, primary_key=True, index=True)
+    entity_id = Column(Integer, default=1, index=True, comment="企业ID (多租户隔离 2026-09-03)")
     event_type = Column(String(30), nullable=False, comment="事件类型: kpi_change/alert/decision/plan/map/import/user_action")
     event_level = Column(String(20), default="info", comment="info/warning/important/critical")
     source = Column(String(50), nullable=True, comment="来源: operation_log/api/erp_sync/manual")
@@ -47,6 +48,7 @@ class KnowledgeSummary(Base):
     __tablename__ = "knowledge_summaries"
 
     id = Column(Integer, primary_key=True, index=True)
+    entity_id = Column(Integer, default=1, index=True, comment="企业ID (多租户隔离 2026-09-03)")
     level = Column(String(20), nullable=False, comment="摘要层级: daily/weekly/monthly/cumulative")
     period_key = Column(String(20), nullable=False, comment="期间标识: 2026-06-12 / 2026-W24 / 2026-06 / cumulative")
     title = Column(String(300), nullable=False, comment="摘要标题")

backend/app/models/knowledge_article.py

@@ -12,6 +12,7 @@ class KnowledgeArticle(Base):
     __tablename__ = "knowledge_articles"
 
     id = Column(Integer, primary_key=True, index=True)
+    entity_id = Column(Integer, nullable=True, index=True, comment="企业ID: NULL=全局共享(系统教学), 有值=企业专属 (多租户隔离 2026-09-03)")
     title = Column(String(200), nullable=False, comment="文章标题")
     summary = Column(String(500), nullable=True, comment="一句话摘要")
     content = Column(Text, nullable=False, comment="文章正文（支持Markdown）")