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-core/src/test_helpers.rs

@@ -0,0 +1,37 @@
+//! 测试基础设施 — 事务回滚模式解决并行化问题
+//!
+//! 每个测试在独立事务中执行，测试结束自动回滚，无数据残留。
+//! 多个测试共享同一个数据库连接池，无连接竞争。
+
+use sea_orm::{
+    ConnectOptions, Database, DatabaseConnection, DatabaseTransaction, TransactionTrait,
+};
+use std::sync::OnceLock;
+use tokio::sync::OnceCell;
+
+static DB_POOL: OnceCell<DatabaseConnection> = OnceCell::const_new();
+static DB_URL: OnceLock<String> = OnceLock::new();
+
+fn db_url() -> String {
+    DB_URL
+        .get_or_init(|| {
+            std::env::var("TEST_DATABASE_URL")
+                .unwrap_or_else(|_| "postgres://erp:erp@localhost:5432/erp_test".into())
+        })
+        .clone()
+}
+
+async fn db_pool() -> &'static DatabaseConnection {
+    DB_POOL
+        .get_or_init(|| async {
+            let opt = ConnectOptions::new(db_url()).max_connections(5).to_owned();
+            Database::connect(opt).await.expect("测试数据库连接失败")
+        })
+        .await
+}
+
+/// 创建测试用事务。测试结束自动回滚，无数据残留。
+pub async fn test_txn() -> DatabaseTransaction {
+    let pool = db_pool().await;
+    pool.begin().await.expect("测试事务创建失败")
+}