Allow AI Context provider/model setting to be explicitly unset
Handling this in:
#3586159
**Description:**
The AI Context general settings page currently uses the AI provider configuration element for `AI Provider/Model`. When no module-specific provider/model is saved, the element visually falls back to the AI module’s core default provider. This makes it look like AI Context has a provider configured and does not give administrators an obvious way to explicitly unset provider/model for AI Context.
AI Context should support an explicit “No provider” state so conditional subcontext can be disabled intentionally unless a provider/model is configured for this module.
**Scope:**
- Add a “No provider” option to the AI Context `AI Provider/Model` setting.
- Ensure the empty option is selected when `ai_context.settings:provider_config.provider_id` and `model_id` are empty.
- Ensure saving “No provider” persists empty `provider_id` and `model_id`.
- Preserve existing validation that prevents clearing provider/model while published conditional subcontext items exist.
- Add/update tests for rendering and saving the empty provider state.
**Acceptance criteria:**
- Admins can explicitly select “No provider” on the AI Context general settings page.
- Empty AI Context provider config does not visually fall back to the AI core default provider.
- Saving “No provider” clears AI Context’s provider/model config.
- Clearing provider/model is still blocked or warned when published conditional subcontext items depend on it.
- Tests cover the empty provider option and saved config behavior.
[x] AI Assisted Issue
issue