ClearChat Home v1.3.0 Theme Release

Changes:
- Added Light / Dark / System theme mode in Settings.
- Admin panel now follows the selected theme.
- Public chat widget now follows the selected theme.
- System mode follows the visitor/operator browser OS preference.
- Widget color palette continues to control the chat button/header in all themes.
- Version bumped to 1.3.0-home.
- Settings API now exposes theme mode, offline form state, and sound setting.
- Public embed script refreshed to include close button, offline form, visitor reply sound support, and theme support.

Patch notes:
- This patch does not include includes/config.php, install/, database/schema.sql, or backups/.
- Hard refresh admin and public pages after applying.
