Refactor layout and navigation components; remove theme toggler

- Updated layout.tsx to remove the ThemeProvider and directly include Analytics, SpeedInsights, and Navigation components.
- Removed ThemeToggler component from Navigation.
- Adjusted global CSS to use media queries for dark theme styles instead of data attributes.
- Cleaned up package.json by removing the next-themes dependency.

package.json

@@ -33,7 +33,6 @@
     "geist": "^1.3.1",
     "lucide-react": "^0.454.0",
     "next": "^15.0.2",
-    "next-themes": "^0.3.0",
     "pdfjs-dist": "^4.9.155",
     "radix-ui": "^1.0.1",
     "react": "^18.3.1",