- Add `Setting` model to Prisma schema for storing API keys and model configs.
- Implement `SettingService` and API for managing application settings.
- Refactor `src/service/ai.ts` to `UnifiedAIService` supporting dynamic OpenAI and Google provider selection.
- Add Settings page (`src/ui/pages/Settings.tsx`) to configure providers and default models.
- Update `AppSidebar` to include Settings, use text-under-icon style, and increase icon size.
- Update `Layout` to move "Forgery" title to header and add GitHub link.
- Add unit tests for `SettingService` and `UnifiedAIService`.
