[FEATURE]:Problems with adding third-party API providers

Feature hasn't been suggested before.

• I have verified this feature I'm about to request hasn't been suggested before.

Describe the enhancement you want to request

1. In the desktop version, when adding a custom API provider, after filling in the API endpoint and key, the model list cannot be fetched automatically. Models must be added manually. Some providers don't offer a model list page — the models can only be retrieved via API. However, the config cannot be saved without adding models manually.

2. Even after the configuration is complete, there is no way to modify it in the UI. If a manually entered model ID is wrong, it cannot be corrected. The same goes for changing the API key — the only option is to delete and re-add the provider. (Or maybe I just missed how to do it.)

3. Because of the above issues, the management logic for third-party APIs in the desktop app feels unintuitive (just my personal opinion).