fix: admin dashboard feature

[Flash303]

This pull request improves the server favicon override functionality in the admin UI by making the favicon state more reliable, preventing stale image previews, and enhancing the user experience for uploading or removing favicons. The changes also add a new field to the server schema to better track favicon overrides.

Favicon override improvements:

• The favicon override state in UpdateFaviconModal now relies on the new forced_favicon field rather than last_favicon, ensuring accurate detection of whether a server has a custom favicon. [1] [2]
• Added a module-level faviconCacheVersion variable that increments after each successful favicon update, forcing the browser to fetch the latest icon and preventing stale preview images due to cache. [1] [2] [3]
• The favicon preview now uses the server's icon URL with a cache-busting query parameter, and the UI disables the save button unless there are actual changes to submit. [1] [2] [3]

Schema update:

• Added a new forced_favicon boolean field to the ServerSchema to reliably indicate if a server has a custom favicon override.

UI/UX enhancements:

• Improved logic for enabling/disabling the reset button and submit button, and clarified when the favicon preview and empty state message are shown. [1] [2] [3]
• Updated image upload and removal logic to ensure consistent state management and preview updates. [1] [2]

These changes make favicon management in the admin interface more robust and user-friendly.