feat: Enhanced developer tools UX with visual improvements

- Fixed StructuredEditor auto-type detection to only trigger on empty fields
- Made array keys readonly with proper index display and full-width value inputs
- Enhanced PHP unserialize to handle empty strings, NULL values, and complex data
- Added JSON to CSV support for single objects as Key-Value format
- Upgraded DiffTool with react-diff-view for professional GitHub-style diffs
- Added theme-synchronized diff colors with proper contrast in light/dark modes
- Implemented red/green text on matching backgrounds for optimal readability

package.json

@@ -21,6 +21,7 @@
     "papaparse": "^5.4.1",
     "react": "^18.2.0",
     "react-codemirror2": "^8.0.1",
+    "react-diff-view": "^3.3.2",
     "react-dom": "^18.2.0",
     "react-router-dom": "^6.3.0",
     "react-scripts": "5.0.1",