refactor(proxy): simplify provider selection to use is_current directly

Changes:
- Modify provider_router to select provider based on is_current flag
  instead of is_proxy_target queue
- Remove proxy target toggle UI from ProviderCard
- Remove proxyPriority and allProviders props from ProviderList
- Remove isProxyTarget prop from ProviderHealthBadge
- Use start_with_takeover() for auto-start to ensure proper setup

This simplifies the proxy architecture by directly using the current
provider for proxying, eliminating the need for separate proxy target
management. Switching providers now immediately takes effect in proxy
mode.

src-tauri/src/lib.rs

@@ -530,7 +530,7 @@ pub fn run() {
                     Ok(config) => {
                         if config.enabled {
                             log::info!("代理服务配置为启用，正在启动...");
-                            match state.proxy_service.start().await {
+                            match state.proxy_service.start_with_takeover().await {
                                 Ok(info) => log::info!(
                                     "代理服务器自动启动成功: {}:{}",
                                     info.address,

src-tauri/src/proxy/provider_router.rs

@@ -30,58 +30,42 @@ impl ProviderRouter {
     /// 选择可用的供应商（支持故障转移）
     /// 返回按优先级排序的可用供应商列表
     pub async fn select_providers(&self, app_type: &str) -> Result<Vec<Provider>, AppError> {
-        // 1. 获取所有启用代理的供应商
-        let providers = self.db.get_proxy_targets(app_type).await?;
+        // 直接获取当前选中的供应商（基于 is_current 字段）
+        let current_id = self.db.get_current_provider(app_type)?
+            .ok_or_else(|| AppError::Config(
+                format!("No current provider for {}", app_type)
+            ))?;
 
-        if providers.is_empty() {
-            return Err(AppError::Config(
-                "No proxy target providers configured".to_string(),
-            ));
-        }
-
-        log::debug!(
-            "Found {} proxy target providers for app_type: {}",
-            providers.len(),
-            app_type
-        );
-
-        // 2. 按 sort_index 排序（已经在数据库查询中排序了）
-        let sorted_providers: Vec<_> = providers.into_values().collect();
-
-        // 3. 过滤可用的供应商（检查熔断器状态）
-        let mut available_providers = Vec::new();
-
-        for provider in sorted_providers {
-            let circuit_key = format!("{}:{}", app_type, provider.id);
-            let breaker = self.get_or_create_circuit_breaker(&circuit_key).await;
-
-            if breaker.allow_request().await {
-                log::debug!(
-                    "Provider {} is available (circuit state: {:?})",
-                    provider.id,
-                    breaker.get_state().await
-                );
-                available_providers.push(provider);
-            } else {
-                log::warn!(
-                    "Provider {} is unavailable (circuit breaker open)",
-                    provider.id
-                );
-            }
-        }
-
-        if available_providers.is_empty() {
-            return Err(AppError::Config(
-                "All proxy target providers are unavailable (circuit breakers open)".to_string(),
-            ));
-        }
+        let providers = self.db.get_all_providers(app_type)?;
+        let provider = providers.get(&current_id)
+            .ok_or_else(|| AppError::Config(
+                format!("Current provider {} not found", current_id)
+            ))?
+            .clone();
 
         log::info!(
-            "Selected {} available providers for failover chain",
-            available_providers.len()
+            "[{}] Selected current provider: {} ({})",
+            app_type,
+            provider.name,
+            provider.id
         );
 
-        Ok(available_providers)
+        // 检查熔断器状态
+        let circuit_key = format!("{}:{}", app_type, provider.id);
+        let breaker = self.get_or_create_circuit_breaker(&circuit_key).await;
+
+        if !breaker.allow_request().await {
+            log::warn!(
+                "Provider {} is unavailable (circuit breaker open)",
+                provider.id
+            );
+            return Err(AppError::Config(
+                format!("Current provider {} is unavailable (circuit breaker open)", provider.name)
+            ));
+        }
+
+        // 返回单个供应商（保留 Vec 接口以兼容现有代码）
+        Ok(vec![provider])
     }
 
     /// 记录供应商请求结果

src-tauri/src/services/provider/mod.rs

@@ -206,14 +206,17 @@ impl ProviderService {
                 id
             );
 
-            // Update database is_current (proxy server reads this)
+            // Update database is_current
             state.db.set_current_provider(app_type.as_str(), id)?;
 
+            // 同时更新 is_proxy_target（代理路由器使用此字段选择供应商）
+            state.db.set_proxy_target_provider(app_type.as_str(), id)?;
+
             // Update local settings for consistency
             crate::settings::set_current_provider(&app_type, Some(id))?;
 
             // Note: No Live config write, no MCP sync
-            // The proxy server will route requests to the new provider
+            // The proxy server will route requests to the new provider via is_proxy_target
             return Ok(());
         }