refactor(ui): use tokenlens as sole model source, remove provider listModels

Remove the per-provider listModels API (GET /providers/:id/models) and all
four provider implementations (OpenAI Compatible, OpenAI Responses, Anthropic,
Gemini). ModelCombobox now only shows tokenlens suggestions (tagged '推荐') plus
free-form custom input — no more unfiltered 'API' models from provider SDKs.

Fixes: switching provider type in ProviderDialog no longer shows stale models
from the original provider's API.

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-opencode)

frontend/src/components/llm/ProviderDialog.tsx

@@ -134,7 +134,6 @@ function ProviderDialogInner({ onOpenChange, provider }: Omit<ProviderDialogProp
           <div className="space-y-2">
             <Label htmlFor="defaultModel">默认模型 <span className="text-red-500">*</span></Label>
             <ModelCombobox
-              providerId={provider?.hasKey ? provider.id : null}
               providerType={type}
               value={defaultModel}
               onChange={setDefaultModel}