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/ProvidersPanel.tsx

@@ -406,14 +406,6 @@ export function ProvidersPanel({ onClose, responsive = false }: ProvidersPanelPr
                       </div>
                     )}
 
-                    {/* API Key Env Var */}
-                    {detail.apiKeyEnvVar && (
-                      <div className="text-xs">
-                        <span className="text-fg-muted">API Key Env:</span>{' '}
-                        <code className="text-fg-secondary bg-surface-subtle px-1 rounded">{detail.apiKeyEnvVar}</code>
-                      </div>
-                    )}
-
                     {/* Models */}
                     <div className="space-y-2">
                       <div className="flex items-center justify-between">
@@ -688,14 +680,6 @@ export function ProvidersPanel({ onClose, responsive = false }: ProvidersPanelPr
                       placeholder="http://localhost:11434/v1"
                     />
                   </div>
-                  <div>
-                    <label className="text-xs text-fg-muted">API Key Env Var (optional)</label>
-                    <Input
-                      value={newProvider.apiKeyEnvVar || ''}
-                      onChange={(e) => setNewProvider((p) => ({ ...p, apiKeyEnvVar: e.target.value }))}
-                      placeholder="OLLAMA_API_KEY"
-                    />
-                  </div>
                 </div>
                 <div className="flex justify-end gap-2 pt-2">
                   <Button variant="ghost" onClick={() => setShowAddProvider(false)}>