[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

首先，将 CLI 的“Add a provider”流程与 issue 中描述的 Desktop Settings 或 model-picker 流程进行比较，包括与 #25 相关的 provider 配置和 session-sync 行为。定义已知 provider、自定义 provider ID、base URL 和 API key 应如何表示。完成标准是 Desktop 能够在 Linux 上以与所请求 CLI 功能相当的方式添加并复用 provider。