feat: Add AI provider settings and update UI layout

- 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`.

package.json

@@ -30,11 +30,14 @@
     "framer-motion": "^12.33.0",
     "hono": "^4.11.8",
     "lucide-react": "^0.563.0",
+    "next-themes": "^0.4.6",
+    "openai": "^6.18.0",
     "radix-ui": "^1.4.3",
     "react": "^19.2.4",
     "react-dom": "^19.2.4",
     "react-router-dom": "^7.13.0",
     "sharp": "^0.34.5",
+    "sonner": "^2.0.7",
     "tailwind-merge": "^3.4.0",
     "tailwindcss": "^4.1.18",
     "tw-animate-css": "^1.4.0",