[Feature]: Add custom models/providers from Telegram

[ardiannurcahya]

Problem

It would be useful to add custom models or providers directly from the Telegram bot.

I know this can already be done by asking OpenCode to edit the config, but having a simple UI in Telegram would make remote setup more convenient.

Proposal

Maybe add an "Add Custom Model" option in the model picker, with fields like:

• Provider
• Base URL
• Model ID
• Context limit
• Output limit

After saving, the new model could appear directly in the model picker.

Done criteria (optional)

• Can add a custom model/provider from Telegram.
• Basic fields like Base URL, Model ID, and context limit can be set.
• The new model shows up in the model picker after saving.