fix(proxy): support system proxy fallback and provider-level proxy config

- Remove no_proxy() calls in http_client.rs to allow system proxy fallback
- Add get_for_provider() to build HTTP client with provider-specific proxy
- Update forwarder.rs and stream_check.rs to use provider proxy config
- Fix EditProviderDialog.tsx to include provider.meta in useMemo deps
- Add useEffect in ProviderAdvancedConfig.tsx to sync expand state

Fixes #636
Fixes #583

src/components/providers/EditProviderDialog.tsx

@@ -129,8 +129,8 @@ export function EditProviderDialog({
     };
   }, [
     provider?.id, // 只依赖 ID，provider 对象更新不会触发重新计算
+    provider?.meta, // 需要依赖 meta 以便正确初始化 testConfig 和 proxyConfig
     initialSettingsConfig,
-    // 注意：不依赖 provider 的其他字段，防止表单重置
   ]);
 
   const handleSubmit = useCallback(