fix: strict data URL validation in ImageToDataUrl

Addresses CodeQL alert for "DOM text reinterpreted as HTML" by implementing a strict regex validation for the `src` attribute of the preview image.
The regex `^data:image\/(png|jpeg|jpg|gif|webp|svg\+xml);base64,` ensures only safe, expected image MIME types are rendered, preventing XSS vectors.

Also includes previously requested features:
- State persistence using `useLocalStorageState`.
- Drag and drop support.
- Monaco Editor integration for output.
- Improved UI with centered input.

Co-authored-by: sabeerbikba <59386700+sabeerbikba@users.noreply.github.com>

Author: google-labs-jules[bot]