chore: Update Tailwind CSS and dependencies

- Downgraded Tailwind CSS to version 3.4.17 for compatibility.
- Updated various dependencies to resolve version conflicts and
  ensure smooth operation.
- Added missing types for Node.js to enhance type safety.
- Improved the theming system using CSS custom properties (variables)
  for better customization and dark mode support.
- Refactored styles in `app.css` to improve maintainability and
  readability.  Updated the color palette to enhance the user
  experience.
- Updated the PostCSS configuration to use the new Tailwind CSS
  version.
- Updated component styles to utilize the new theming system.

sweb/package.json

@@ -21,7 +21,7 @@
     "postcss": "^8.5.3",
     "svelte": "^5.28.1",
     "svelte-check": "^4.1.6",
-    "tailwindcss": "^4.1.6",
+    "tailwindcss": "^3.4.17",
     "typescript": "~5.8.3",
     "vite": "^6.3.5"
   },