fix(health): 添加 GET 单条轮播图端点 — 修复 Switch 切换 405

后端 /health/banners/{id} 路由只注册了 PUT/DELETE，缺少 GET handler。
前端 bannerApi.get(id) 调用时返回 405 Method Not Allowed，导致轮播图
状态切换失败。新增 banner_service::get_banner + banner_handler::get_banner
+ BannerNotFound 错误类型 + 路由注册。

crates/erp-health/src/error.rs

@@ -107,6 +107,9 @@ pub enum HealthError {
     #[error("媒体文件夹不存在")]
     MediaFolderNotFound,
 
+    #[error("轮播图不存在")]
+    BannerNotFound,
+
     #[error("状态转换无效: {0}")]
     InvalidStatusTransition(String),
 
@@ -157,7 +160,8 @@ impl From<HealthError> for AppError {
             | HealthError::PatientAssignmentNotFound
             | HealthError::HandoffLogNotFound
             | HealthError::MediaNotFound
-            | HealthError::MediaFolderNotFound => AppError::NotFound(err.to_string()),
+            | HealthError::MediaFolderNotFound
+            | HealthError::BannerNotFound => AppError::NotFound(err.to_string()),
             HealthError::ScheduleFull => AppError::Validation(err.to_string()),
             HealthError::InvalidStatusTransition(s) => AppError::Validation(s),
             HealthError::VersionMismatch => AppError::VersionMismatch,

crates/erp-health/src/handler/banner_handler.rs

@@ -49,6 +49,21 @@ where
     Ok(Json(ApiResponse::ok(result)))
 }
 
+/// GET /health/banners/{id} — 获取单个轮播图
+pub async fn get_banner<S>(
+    State(state): State<HealthState>,
+    Extension(ctx): Extension<TenantContext>,
+    Path(id): Path<uuid::Uuid>,
+) -> Result<Json<ApiResponse<BannerResp>>, AppError>
+where
+    HealthState: FromRef<S>,
+    S: Clone + Send + Sync + 'static,
+{
+    require_permission(&ctx, "health.banners.list")?;
+    let result = banner_service::get_banner(&state, ctx.tenant_id, id).await?;
+    Ok(Json(ApiResponse::ok(result)))
+}
+
 /// POST /health/banners — 创建轮播图
 pub async fn create_banner<S>(
     State(state): State<HealthState>,

crates/erp-health/src/routes/media.rs

@@ -55,6 +55,8 @@ where
         )
         .route(
             "/health/banners/{id}",
-            axum::routing::put(banner_handler::update_banner).delete(banner_handler::delete_banner),
+            axum::routing::get(banner_handler::get_banner)
+                .put(banner_handler::update_banner)
+                .delete(banner_handler::delete_banner),
         )
 }

crates/erp-health/src/service/banner_service.rs

@@ -62,6 +62,23 @@ pub async fn list_banners(
     Ok(result)
 }
 
+/// 获取单个轮播图
+pub async fn get_banner(
+    state: &HealthState,
+    tenant_id: Uuid,
+    banner_id: Uuid,
+) -> HealthResult<BannerResp> {
+    let b = banner::Entity::find_by_id(banner_id)
+        .filter(banner::Column::TenantId.eq(tenant_id))
+        .filter(banner::Column::DeletedAt.is_null())
+        .one(&state.db)
+        .await?
+        .ok_or(HealthError::BannerNotFound)?;
+
+    let media_map = load_media_map(state, &[b.media_item_id]).await?;
+    Ok(banner_to_resp(&b, &media_map))
+}
+
 /// 创建轮播图
 pub async fn create_banner(
     state: &HealthState,