fix(server+health): 修复路由 middleware 泄漏 — FHIR/Gateway 改用 .nest() 隔离

Axum 的 .merge() 会将子 Router 的 middleware 泄漏到整个路由树，
导致 FHIR OAuth middleware 和 Gateway auth middleware 拦截所有请求。

修复方式：
- fhir_routes 内部路径去掉 /fhir 前缀，main.rs 用 .nest("/fhir", ...) 注册
- gateway_routes 内部路径去掉 /health/gateway 前缀，main.rs 用 .nest("/health/gateway", ...) 注册
- 透析患者查询表名 patients → patient（与 Entity 一致）

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

crates/erp-dialysis/src/service/dialysis_service.rs

@@ -75,7 +75,7 @@ pub async fn create_dialysis_record(
     // 患者存在性校验
     let patient_sql = sea_orm::Statement::from_sql_and_values(
         sea_orm::DatabaseBackend::Postgres,
-        "SELECT EXISTS(SELECT 1 FROM patients WHERE id = $1 AND tenant_id = $2 AND deleted_at IS NULL)",
+        "SELECT EXISTS(SELECT 1 FROM patient WHERE id = $1 AND tenant_id = $2 AND deleted_at IS NULL)",
         [req.patient_id.into(), tenant_id.into()],
     );
     if let Ok(row) = state.db.query_one(patient_sql).await {