feat(plugin): P1 跨插件数据引用系统 — 后端 Phase 1-3

实现跨插件实体引用的基础后端能力：

Phase 1 — Manifest 扩展 + Entity Registry 数据层:
- PluginField 新增 ref_plugin/ref_fallback_label 支持跨插件引用声明
- PluginRelation 新增 name/relation_type/display_field（CRM 已在用的字段）
- PluginEntity 新增 is_public 标记可被其他插件引用的实体
- 数据库迁移：plugin_entities 新增 manifest_id + is_public 列 + 索引
- SeaORM Entity 和 install 流程同步更新

Phase 2 — 后端跨插件引用解析 + 校验:
- data_service: 新增 resolve_cross_plugin_entity/is_plugin_active 函数
- validate_ref_entities: 支持 ref_plugin 字段，目标插件未安装时跳过校验（软警告）
- host.rs: HostState 新增 cross_plugin_entities 映射，db_query 支持点分记号
- engine.rs: execute_wasm 自动构建跨插件实体映射

Phase 3 — API 端点:
- POST /plugins/{id}/{entity}/resolve-labels 批量标签解析
- GET /plugin-registry/entities 公开实体注册表查询

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

@@ -37,6 +37,8 @@ mod m20260417_000034_seed_plugin_permissions;
 mod m20260418_000035_pg_trgm_and_entity_columns;
 mod m20260418_000036_add_data_scope_to_role_permissions;
 mod m20260419_000037_create_user_departments;
+mod m20260419_000038_fix_crm_permission_codes;
+mod m20260419_000039_entity_registry_columns;
 
 pub struct Migrator;
 
@@ -81,6 +83,8 @@ impl MigratorTrait for Migrator {
             Box::new(m20260418_000035_pg_trgm_and_entity_columns::Migration),
             Box::new(m20260418_000036_add_data_scope_to_role_permissions::Migration),
             Box::new(m20260419_000037_create_user_departments::Migration),
+            Box::new(m20260419_000038_fix_crm_permission_codes::Migration),
+            Box::new(m20260419_000039_entity_registry_columns::Migration),
         ]
     }
 }

crates/erp-server/migration/src/m20260419_000039_entity_registry_columns.rs

@@ -0,0 +1,51 @@
+use sea_orm_migration::prelude::*;
+
+#[derive(DeriveMigrationName)]
+pub struct Migration;
+
+#[async_trait::async_trait]
+impl MigrationTrait for Migration {
+    async fn up(&self, manager: &SchemaManager) -> Result<(), DbErr> {
+        // plugin_entities 新增 manifest_id 列 — 避免跨插件查询时 JOIN plugins 表
+        manager
+            .get_connection()
+            .execute_unprepared(
+                r#"
+ALTER TABLE plugin_entities
+ADD COLUMN IF NOT EXISTS manifest_id TEXT NOT NULL DEFAULT '';
+
+ALTER TABLE plugin_entities
+ADD COLUMN IF NOT EXISTS is_public BOOLEAN NOT NULL DEFAULT false;
+
+-- 回填 manifest_id（从 plugins.manifest_json 提取 metadata.id）
+UPDATE plugin_entities pe
+SET manifest_id = COALESCE(p.manifest_json->'metadata'->>'id', '')
+FROM plugins p
+WHERE pe.plugin_id = p.id AND pe.deleted_at IS NULL;
+
+-- 跨插件实体查找索引
+CREATE INDEX IF NOT EXISTS idx_plugin_entities_cross_ref
+ON plugin_entities (manifest_id, entity_name, tenant_id)
+WHERE deleted_at IS NULL;
+"#,
+            )
+            .await?;
+
+        Ok(())
+    }
+
+    async fn down(&self, manager: &SchemaManager) -> Result<(), DbErr> {
+        manager
+            .get_connection()
+            .execute_unprepared(
+                r#"
+DROP INDEX IF EXISTS idx_plugin_entities_cross_ref;
+ALTER TABLE plugin_entities DROP COLUMN IF EXISTS is_public;
+ALTER TABLE plugin_entities DROP COLUMN IF EXISTS manifest_id;
+"#,
+            )
+            .await?;
+
+        Ok(())
+    }
+}