feat(ai+db): 知识库 3 表迁移 + Entity — rules/references/guides

Phase 3 Task 21:
- ai_knowledge_rules: L1 规则表（条件表达式 + 动作文本）
- ai_knowledge_references: L2 参考表（摘要 + pgvector 嵌入）
- ai_knowledge_guides: L3 指南表（全文 + pgvector 嵌入）

crates/erp-server/migration/src/lib.rs

@@ -119,6 +119,9 @@ mod m20260505_000116_seed_missing_health_menus;
 mod m20260505_000117_create_ai_tenant_configs;
 mod m20260505_000118_create_ai_analysis_queue;
 mod m20260505_000119_enable_pgvector;
+mod m20260505_000120_create_ai_knowledge_rules;
+mod m20260505_000121_create_ai_knowledge_references;
+mod m20260505_000122_create_ai_knowledge_guides;
 
 pub struct Migrator;
 
@@ -245,6 +248,9 @@ impl MigratorTrait for Migrator {
             Box::new(m20260505_000117_create_ai_tenant_configs::Migration),
             Box::new(m20260505_000118_create_ai_analysis_queue::Migration),
             Box::new(m20260505_000119_enable_pgvector::Migration),
+            Box::new(m20260505_000120_create_ai_knowledge_rules::Migration),
+            Box::new(m20260505_000121_create_ai_knowledge_references::Migration),
+            Box::new(m20260505_000122_create_ai_knowledge_guides::Migration),
         ]
     }
 }