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)
Add complete Web UI for LLM provider configuration: provider list with
enable/disable toggles, add/edit dialog, connection testing with result
display, role assignment cards, and model combobox with API/recommended/custom
tags. All labels in Chinese. Add description prop to SelectItem for
Radix Select rendering fix. Register route and nav link.
Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-opencode)
