Allow disabling individual built-in models

Feature request

I'd like to be able to disable individual built-in Command Code models from the /model menu.

Right now, ~/.commandcode/providers.json supports disabling an entire BYOK provider with "disabled": true, but there doesn't seem to be a supported way to hide or disable one specific built-in model.

I'd like a configuration option at user scope that lets me disable specific models without removing access to the rest of the catalog. This would make the model picker less cluttered and make it easier to prevent accidental selection of models I don't want to use.

Suggested behavior

• Support an allowlist or denylist for built-in model IDs.
• Apply it to the /model menu and model selection shortcuts.
• Keep the setting at user scope so it applies across projects.
• Keep the current BYOK provider-level disabled behavior unchanged.

Example

{
  "disabledModels": ["some/model-id"]
}

從 ~/.commandcode/providers.json 所代表的使用者範圍設定開始，接著追蹤 /model 選單和模型選擇快速鍵。檢查內建模型 ID 和提供者層級的停用設定如何載入與篩選。完成的標準是：使用者可以跨專案停用選定的內建模型，同時現有的 BYOK 提供者行為維持不變。