refactor: 清理未使用的类型定义和接口字段

- 移除 Provider 相关的 apiKeyEnvVar 字段（未实现的功能）
- 清理 Server routes 中未使用的 Core 类型导入
- 清理 UI Message 接口中未使用的 metadata 字段

packages/ui/src/components/ProviderEditor.tsx

@@ -54,7 +54,6 @@ export function ProviderEditor({
 
   // Form state
   const [apiKey, setApiKey] = useState('');
-  const [apiKeyEnvVar, setApiKeyEnvVar] = useState('');
   const [baseUrl, setBaseUrl] = useState('');
   const [enabled, setEnabled] = useState(true);
 
@@ -84,7 +83,6 @@ export function ProviderEditor({
           const config = result.data.config;
           // API key is not returned for security, but we show if it's configured via hasApiKey
           setApiKey('');
-          setApiKeyEnvVar(result.data.apiKeyEnvVar || '');
           setBaseUrl(config.baseUrl || result.data.baseUrl || '');
           setEnabled(config.enabled !== false);
         } else {
@@ -114,9 +112,6 @@ export function ProviderEditor({
       if (apiKey.trim()) {
         config.apiKey = apiKey;
       }
-      if (apiKeyEnvVar.trim() && apiKeyEnvVar !== provider?.apiKeyEnvVar) {
-        config.apiKeyEnvVar = apiKeyEnvVar;
-      }
       if (baseUrl.trim() && baseUrl !== provider?.baseUrl) {
         config.baseUrl = baseUrl;
       }
@@ -336,20 +331,6 @@ export function ProviderEditor({
                     )}
                   </div>
 
-                  {/* API Key Env Var */}
-                  <div>
-                    <label className="block text-xs text-fg-muted mb-1">
-                      Environment Variable (alternative)
-                    </label>
-                    <Input
-                      value={apiKeyEnvVar}
-                      onChange={(e) => setApiKeyEnvVar(e.target.value)}
-                      placeholder={provider?.apiKeyEnvVar || 'PROVIDER_API_KEY'}
-                    />
-                    <p className="text-xs text-fg-subtle mt-1">
-                      If no API key is set, this env var will be used
-                    </p>
-                  </div>
                 </div>
 
                 {/* Base URL Section */}