fix(proxy): update live backup when hot-switching provider in proxy mode

When proxy is active, switching providers only updated the database flags
but not the live backup. This caused the wrong provider config to be
restored when stopping the proxy.

Added `update_live_backup_from_provider()` method to ProxyService that
generates backup from provider's settings_config instead of reading from
live files (which are already taken over by proxy).

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

@@ -206,6 +206,11 @@ impl ProviderService {
                 id
             );
 
+            // 获取新供应商的完整配置（用于更新备份）
+            let provider = providers
+                .get(id)
+                .ok_or_else(|| AppError::Message(format!("供应商 {id} 不存在")))?;
+
             // Update database is_current
             state.db.set_current_provider(app_type.as_str(), id)?;
 
@@ -215,6 +220,14 @@ impl ProviderService {
             // Update local settings for consistency
             crate::settings::set_current_provider(&app_type, Some(id))?;
 
+            // 更新 Live 备份（确保代理关闭时恢复正确的供应商配置）
+            futures::executor::block_on(
+                state
+                    .proxy_service
+                    .update_live_backup_from_provider(app_type.as_str(), provider),
+            )
+            .map_err(|e| AppError::Message(format!("更新 Live 备份失败: {e}")))?;
+
             // Note: No Live config write, no MCP sync
             // The proxy server will route requests to the new provider via is_proxy_target
             return Ok(());