feat(ai): 添加 Provider 管理 API 端点

GET /ai/providers — 列出已注册提供商
GET /ai/providers/health — 各提供商健康状态
GET /ai/quota/summary — 租户配额使用摘要

crates/erp-ai/src/module.rs

@@ -246,5 +246,17 @@ impl AiModule {
                 "/ai/dialysis/risk-assessment",
                 axum::routing::post(crate::handler::assess_dialysis_risk),
             )
+            .route(
+                "/ai/providers/health",
+                axum::routing::get(crate::handler::provider_health),
+            )
+            .route(
+                "/ai/providers",
+                axum::routing::get(crate::handler::provider_names),
+            )
+            .route(
+                "/ai/quota/summary",
+                axum::routing::get(crate::handler::quota_summary),
+            )
     }
 }