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-plugin/src/manifest.rs

@@ -47,6 +47,8 @@ pub struct PluginEntity {
     pub relations: Vec<PluginRelation>,
     #[serde(default)]
     pub data_scope: Option<bool>,  // 是否启用行级数据权限
+    #[serde(default)]
+    pub is_public: Option<bool>,   // 是否可被其他插件引用
 }
 
 /// 字段校验规则
@@ -87,6 +89,8 @@ pub struct PluginField {
     pub no_cycle: Option<bool>,               // 禁止循环引用
     #[serde(default)]
     pub scope_role: Option<String>,           // 标记为数据权限的"所有者"字段
+    pub ref_plugin: Option<String>,           // 跨插件引用的目标插件 manifest ID（如 "erp-crm"）
+    pub ref_fallback_label: Option<String>,   // 目标插件未安装时的降级显示文本
 }
 
 /// 字段类型
@@ -158,6 +162,8 @@ impl PluginField {
             validation: None,
             no_cycle: None,
             scope_role: None,
+            ref_plugin: None,
+            ref_fallback_label: None,
         }
     }
 }
@@ -186,6 +192,12 @@ pub struct PluginRelation {
     pub entity: String,
     pub foreign_key: String,
     pub on_delete: OnDeleteStrategy,
+    #[serde(default)]
+    pub name: Option<String>,            // 关联名称（UI 显示用）
+    #[serde(default, alias = "type")]
+    pub relation_type: Option<String>,   // "one_to_many" | "many_to_one" | "many_to_many"
+    #[serde(default)]
+    pub display_field: Option<String>,   // 关联记录的显示字段
 }
 
 /// 事件订阅配置
@@ -916,6 +928,98 @@ cascade_filter = "customer_id"
         assert_eq!(contact_field.cascade_filter.as_deref(), Some("customer_id"));
     }
 
+    #[test]
+    fn parse_field_with_cross_plugin_ref() {
+        let toml = r#"
+[metadata]
+id = "erp-inventory"
+name = "进销存"
+version = "0.2.0"
+dependencies = ["erp-crm"]
+
+[schema]
+[[schema.entities]]
+name = "sales_order"
+display_name = "销售订单"
+
+[[schema.entities.fields]]
+name = "customer_id"
+field_type = "uuid"
+display_name = "客户"
+ui_widget = "entity_select"
+ref_plugin = "erp-crm"
+ref_entity = "customer"
+ref_label_field = "name"
+ref_search_fields = ["name", "code"]
+ref_fallback_label = "CRM 客户"
+"#;
+        let manifest = parse_manifest(toml).unwrap();
+        let field = &manifest.schema.unwrap().entities[0].fields[0];
+        assert_eq!(field.ref_plugin.as_deref(), Some("erp-crm"));
+        assert_eq!(field.ref_entity.as_deref(), Some("customer"));
+        assert_eq!(field.ref_label_field.as_deref(), Some("name"));
+        assert_eq!(field.ref_fallback_label.as_deref(), Some("CRM 客户"));
+        assert_eq!(manifest.metadata.dependencies, vec!["erp-crm"]);
+    }
+
+    #[test]
+    fn parse_entity_with_is_public() {
+        let toml = r#"
+[metadata]
+id = "erp-crm"
+name = "CRM"
+version = "0.1.0"
+
+[schema]
+[[schema.entities]]
+name = "customer"
+display_name = "客户"
+is_public = true
+
+[[schema.entities]]
+name = "internal_config"
+display_name = "内部配置"
+"#;
+        let manifest = parse_manifest(toml).unwrap();
+        let entities = &manifest.schema.unwrap().entities;
+        assert_eq!(entities[0].is_public, Some(true));
+        assert_eq!(entities[1].is_public, None);
+    }
+
+    #[test]
+    fn parse_relation_with_name_and_type() {
+        let toml = r#"
+[metadata]
+id = "test"
+name = "Test"
+version = "0.1.0"
+
+[schema]
+[[schema.entities]]
+name = "customer"
+display_name = "客户"
+
+[[schema.entities.fields]]
+name = "code"
+field_type = "string"
+display_name = "编码"
+
+[[schema.entities.relations]]
+entity = "contact"
+foreign_key = "customer_id"
+on_delete = "cascade"
+name = "contacts"
+type = "one_to_many"
+display_field = "name"
+"#;
+        let manifest = parse_manifest(toml).unwrap();
+        let relation = &manifest.schema.unwrap().entities[0].relations[0];
+        assert_eq!(relation.entity, "contact");
+        assert_eq!(relation.name.as_deref(), Some("contacts"));
+        assert_eq!(relation.relation_type.as_deref(), Some("one_to_many"));
+        assert_eq!(relation.display_field.as_deref(), Some("name"));
+    }
+
     #[test]
     fn parse_kanban_page() {
         let toml = r#"