[Feedback]: Desktop lacks support for adding custom providers (parity with CLI `Add a provider`)

What problem are you trying to solve?

In Command Code Desktop (Linux, v0.1.30) there is no equivalent to the CLI v1.54.0 flow for adding custom providers (Add a provider / provider id: ollama, work-llm, openrouter… plus the list with vercel, groq, mistral, xai, together, cerebras, ↓ 184 more).

This is what the flow looks like in the CLI:

# Command Code v1.54.0
# models: muse-spark-1.3-contributor

Add a provider
Pick a known provider below, or type your own id.

provider id: ollama, work-llm, openrouter…
  vercel · https://ai-gateway.vercel.sh/v1
  groq · https://api.groq.com/openai/v1
  mistral · https://api.mistral.ai/v1
  xai · https://api.x.ai/v1
  together · https://api.together.xyz/v1
  cerebras · https://api.cerebras.ai/v1
  ↓ 184 more

In the Desktop app there is no screen/button/command (cmd) to do the same — only the default provider/login can be used, with no way to connect third-party providers (Ollama, OpenRouter, Groq, Together, etc.).

What would improve it?

Parity with the CLI in the Desktop app:

• An "Add a provider" screen/button in Settings (or in the model picker);
• A list of known providers plus a field for a custom provider id + baseURL + API key;
• The same 190+ providers available in the CLI.

What do you do today?

I use CLI v1.54.0 in the terminal to configure the provider, but the configuration is not reflected/reusable in the Desktop app on Linux — TUI/CLI and Desktop flows seem not to sync providers/sessions (related to #25).

Context / Environment

• Desktop: v0.1.30 (latest as of 2026-09-16), Linux
• CLI: v1.54.0 (muse-spark-1.3-contributor)
• Reported on: Linux

Bắt đầu bằng cách so sánh luồng CLI “Add a provider” với luồng Desktop Settings hoặc model-picker được mô tả trong issue, bao gồm cấu hình provider và hành vi session-sync liên quan đến #25. Xác định cách biểu diễn các provider đã biết, các provider ID tùy chỉnh, base URL và API key. Hoàn thành khi Desktop có thể thêm và sử dụng lại các provider với mức tương đương với chức năng CLI được yêu cầu trên Linux.