Add comprehensive dark mode support and fix color consistency

- Add automatic dark/light theme detection via prefers-color-scheme
- Add smooth transitions between theme changes
- Fix color contrast issues with explicit text colors
- Make JSON Data and Query Result boxes static (no color changes)
- Keep only Expression input with error indication (red styling)
- Remove dynamic success/error styling from data input/output areas
- Add proper placeholder and focus state colors for both themes
- Ensure all text remains visible in both light and dark modes
- Clean up unused CSS classes

package-lock.json

@@ -17,7 +17,7 @@
         "react": "^18.2.0",
         "react-dom": "^18.2.0",
         "react-scripts": "^5.0.1",
-        "serve": "^14.2.1",
+        "serve": "^14.2.5",
         "web-vitals": "^3.5.0"
       },
       "engines": {