feat: integrate shadcn components and enable dark mode by default

- Add shadcn/ui components (Button, Input, Card, Progress)
- Replace custom UI elements with shadcn components throughout the app
- Install required dependencies (@radix-ui, lucide-react, class-variance-authority)
- Create utils file for proper component styling
- Enable dark mode as default theme
- Update CSS with proper oklch color system and dark mode variables
- Remove media query for automatic color scheme detection
- Maintain all existing functionality with improved component consistency

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

package.json

@@ -9,19 +9,26 @@
     "lint": "eslint"
   },
   "dependencies": {
+    "@radix-ui/react-progress": "^1.1.7",
+    "@radix-ui/react-slot": "^1.2.3",
+    "class-variance-authority": "^0.7.1",
+    "clsx": "^2.1.1",
+    "lucide-react": "^0.544.0",
+    "next": "15.5.3",
     "react": "19.1.0",
     "react-dom": "19.1.0",
-    "next": "15.5.3"
+    "tailwind-merge": "^3.3.1"
   },
   "devDependencies": {
-    "typescript": "^5",
+    "@eslint/eslintrc": "^3",
+    "@tailwindcss/postcss": "^4",
     "@types/node": "^20",
     "@types/react": "^19",
     "@types/react-dom": "^19",
-    "@tailwindcss/postcss": "^4",
-    "tailwindcss": "^4",
     "eslint": "^9",
     "eslint-config-next": "15.5.3",
-    "@eslint/eslintrc": "^3"
+    "tailwindcss": "^4",
+    "tw-animate-css": "^1.3.8",
+    "typescript": "^5"
   }
 }