refactor(proxy): remove is_proxy_target in favor of failover_queue

- Remove `is_proxy_target` field from Provider struct (Rust & TypeScript)
- Remove related DAO methods: get_proxy_target_provider, set_proxy_target
- Remove deprecated Tauri commands: get_proxy_targets, set_proxy_target
- Add `is_available()` method to CircuitBreaker for availability checks
  without consuming HalfOpen probe permits (used in select_providers)
- Keep `allow_request()` for actual request gating with permit tracking
- Update stream_check to use failover_queue instead of is_proxy_target
- Clean up commented-out reset circuit breaker button in ProviderActions
- Remove unused useProxyTargets and useSetProxyTarget hooks

src-tauri/src/commands/provider.rs

@@ -86,19 +86,6 @@ pub fn switch_provider(
         .map_err(|e| e.to_string())
 }
 
-/// 设置代理目标供应商
-#[tauri::command]
-pub fn set_proxy_target_provider(
-    state: State<'_, AppState>,
-    app: String,
-    id: String,
-) -> Result<bool, String> {
-    let app_type = AppType::from_str(&app).map_err(|e| e.to_string())?;
-    ProviderService::set_proxy_target(state.inner(), app_type, &id)
-        .map(|_| true)
-        .map_err(|e| e.to_string())
-}
-
 fn import_default_config_internal(state: &AppState, app_type: AppType) -> Result<bool, AppError> {
     ProviderService::import_default_config(state, app_type)
 }

src-tauri/src/commands/proxy.rs

@@ -2,7 +2,6 @@
 //!
 //! 提供前端调用的 API 接口
 
-use crate::provider::Provider;
 use crate::proxy::types::*;
 use crate::proxy::{CircuitBreakerConfig, CircuitBreakerStats};
 use crate::store::AppState;
@@ -69,47 +68,6 @@ pub async fn switch_proxy_provider(
 
 // ==================== 故障转移相关命令 ====================
 
-/// 获取代理目标列表
-#[tauri::command]
-pub async fn get_proxy_targets(
-    state: tauri::State<'_, AppState>,
-    app_type: String,
-) -> Result<Vec<Provider>, String> {
-    let db = &state.db;
-    db.get_proxy_targets(&app_type)
-        .await
-        .map_err(|e| e.to_string())
-        .map(|providers| providers.into_values().collect())
-}
-
-/// 设置代理目标
-#[tauri::command]
-pub async fn set_proxy_target(
-    state: tauri::State<'_, AppState>,
-    provider_id: String,
-    app_type: String,
-    enabled: bool,
-) -> Result<(), String> {
-    let db = &state.db;
-
-    // 设置代理目标状态
-    db.set_proxy_target(&provider_id, &app_type, enabled)
-        .await
-        .map_err(|e| e.to_string())?;
-
-    // 如果是禁用代理目标，重置健康状态
-    if !enabled {
-        log::info!(
-            "Resetting health status for provider {provider_id} (app: {app_type}) after disabling proxy target"
-        );
-        if let Err(e) = db.reset_provider_health(&provider_id, &app_type).await {
-            log::warn!("Failed to reset provider health: {e}");
-        }
-    }
-
-    Ok(())
-}
-
 /// 获取供应商健康状态
 #[tauri::command]
 pub async fn get_provider_health(

src-tauri/src/commands/stream_check.rs

@@ -6,6 +6,7 @@ use crate::services::stream_check::{
     HealthStatus, StreamCheckConfig, StreamCheckResult, StreamCheckService,
 };
 use crate::store::AppState;
+use std::collections::HashSet;
 use tauri::State;
 
 /// 流式健康检查（单个供应商）
@@ -44,10 +45,28 @@ pub async fn stream_check_all_providers(
     let providers = state.db.get_all_providers(app_type.as_str())?;
 
     let mut results = Vec::new();
+    let allowed_ids: Option<HashSet<String>> = if proxy_targets_only {
+        let mut ids = HashSet::new();
+        if let Ok(Some(current_id)) = state.db.get_current_provider(app_type.as_str()) {
+            ids.insert(current_id);
+        }
+        if let Ok(queue) = state.db.get_failover_queue(app_type.as_str()) {
+            for item in queue {
+                if item.enabled {
+                    ids.insert(item.provider_id);
+                }
+            }
+        }
+        Some(ids)
+    } else {
+        None
+    };
 
     for (id, provider) in providers {
-        if proxy_targets_only && !provider.is_proxy_target.unwrap_or(false) {
-            continue;
+        if let Some(ids) = &allowed_ids {
+            if !ids.contains(&id) {
+                continue;
+            }
         }
 
         let result = StreamCheckService::check_with_retry(&app_type, &provider, &config)