feat(proxy): implement independent failover queue management

Add a new failover queue system that operates independently from provider
sortIndex, allowing users to configure failover order per app type.

Backend changes:
- Add failover_queue table to schema.rs for persistent storage
- Create dao/failover.rs with CRUD operations for queue management
- Add Tauri commands for queue operations (get, add, remove, reorder, toggle)
- Refactor provider_router.rs select_providers() to use failover queue:
  - Current provider always takes first priority
  - Queue providers ordered by queue_order as fallback
  - Only providers with open circuit breakers are included

Frontend changes:
- Add FailoverQueueItem type to proxy.ts
- Extend failover.ts API with queue management methods
- Add React Query hooks for queue data fetching and mutations
- Create FailoverQueueManager component with drag-and-drop reordering
- Integrate queue management into SettingsPage under "Auto Failover"
- Add i18n translations for zh and en locales

src-tauri/src/commands/failover.rs

@@ -0,0 +1,84 @@
+//! 故障转移队列命令
+//!
+//! 管理代理模式下的故障转移队列
+
+use crate::database::FailoverQueueItem;
+use crate::provider::Provider;
+use crate::store::AppState;
+
+/// 获取故障转移队列
+#[tauri::command]
+pub async fn get_failover_queue(
+    state: tauri::State<'_, AppState>,
+    app_type: String,
+) -> Result<Vec<FailoverQueueItem>, String> {
+    state
+        .db
+        .get_failover_queue(&app_type)
+        .map_err(|e| e.to_string())
+}
+
+/// 获取可添加到故障转移队列的供应商（不在队列中的）
+#[tauri::command]
+pub async fn get_available_providers_for_failover(
+    state: tauri::State<'_, AppState>,
+    app_type: String,
+) -> Result<Vec<Provider>, String> {
+    state
+        .db
+        .get_available_providers_for_failover(&app_type)
+        .map_err(|e| e.to_string())
+}
+
+/// 添加供应商到故障转移队列
+#[tauri::command]
+pub async fn add_to_failover_queue(
+    state: tauri::State<'_, AppState>,
+    app_type: String,
+    provider_id: String,
+) -> Result<(), String> {
+    state
+        .db
+        .add_to_failover_queue(&app_type, &provider_id)
+        .map_err(|e| e.to_string())
+}
+
+/// 从故障转移队列移除供应商
+#[tauri::command]
+pub async fn remove_from_failover_queue(
+    state: tauri::State<'_, AppState>,
+    app_type: String,
+    provider_id: String,
+) -> Result<(), String> {
+    state
+        .db
+        .remove_from_failover_queue(&app_type, &provider_id)
+        .map_err(|e| e.to_string())
+}
+
+/// 重新排序故障转移队列
+#[tauri::command]
+pub async fn reorder_failover_queue(
+    state: tauri::State<'_, AppState>,
+    app_type: String,
+    provider_ids: Vec<String>,
+) -> Result<(), String> {
+    state
+        .db
+        .reorder_failover_queue(&app_type, &provider_ids)
+        .map_err(|e| e.to_string())
+}
+
+/// 设置故障转移队列项的启用状态
+#[tauri::command]
+pub async fn set_failover_item_enabled(
+    state: tauri::State<'_, AppState>,
+    app_type: String,
+    provider_id: String,
+    enabled: bool,
+) -> Result<(), String> {
+    state
+        .db
+        .set_failover_item_enabled(&app_type, &provider_id, enabled)
+        .map_err(|e| e.to_string())
+}

src-tauri/src/commands/mod.rs

@@ -3,6 +3,7 @@
 mod config;
 mod deeplink;
 mod env;
+mod failover;
 mod import_export;
 mod mcp;
 mod misc;
@@ -18,6 +19,7 @@ mod usage;
 pub use config::*;
 pub use deeplink::*;
 pub use env::*;
+pub use failover::*;
 pub use import_export::*;
 pub use mcp::*;
 pub use misc::*;