feat: initialize ERP base platform (extracted from HMS)

- Stripped 11 business crates (health, ai, dialysis, plugins)
- Cleaned AppState, AppConfig, main.rs from business coupling
- Reduced migrations from 169 to 53 (base-only)
- Removed health_provider trait from erp-core
- Removed business integration tests
- Removed gateway rate limiting middleware
- Base capabilities: auth, RBAC, JWT, config, workflow, message, plugin, audit, crypto, RLS, multi-tenant

Cargo check: OK
Cargo test: OK

crates/erp-plugin/src/entity/plugin_entity.rs

@@ -0,0 +1,43 @@
+use sea_orm::entity::prelude::*;
+use serde::{Deserialize, Serialize};
+
+#[derive(Clone, Debug, PartialEq, DeriveEntityModel, Serialize, Deserialize)]
+#[sea_orm(table_name = "plugin_entities")]
+pub struct Model {
+    #[sea_orm(primary_key, auto_increment = false)]
+    pub id: Uuid,
+    pub tenant_id: Uuid,
+    pub plugin_id: Uuid,
+    pub entity_name: String,
+    pub table_name: String,
+    pub schema_json: serde_json::Value,
+    pub manifest_id: String,
+    pub is_public: bool,
+    pub created_at: DateTimeUtc,
+    pub updated_at: DateTimeUtc,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub created_by: Option<Uuid>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub updated_by: Option<Uuid>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub deleted_at: Option<DateTimeUtc>,
+    pub version: i32,
+}
+
+#[derive(Copy, Clone, Debug, EnumIter, DeriveRelation)]
+pub enum Relation {
+    #[sea_orm(
+        belongs_to = "super::plugin::Entity",
+        from = "Column::PluginId",
+        to = "super::plugin::Column::Id"
+    )]
+    Plugin,
+}
+
+impl Related<super::plugin::Entity> for Entity {
+    fn to() -> RelationDef {
+        Relation::Plugin.def()
+    }
+}
+
+impl ActiveModelBehavior for ActiveModel {}