The Admin V3 styles are now the primary styles for the application. This change promotes the `admin_v3` directory to `admin` and archives the old styles.
Changes:
- Renamed `app/webpacker/css/admin_v3` to `app/webpacker/css/admin`.
- Renamed the previous `app/webpacker/css/admin` to `app/webpacker/css/admin_legacy`.
- Moved all files referenced by V3 styles from the legacy directory to the new `admin` directory.
- Updated imports in `all.scss` to distinct local files instead of relative paths.
- Cleaned up `admin_legacy` by removing files that are duplicates (by name or content) of the new admin styles.
- Updated `admin-style-v3` pack to point to the new location.
Completes migration to the new admin v3 styling system by:
- Removing conditional stylesheet inclusion in admin head
- Deleting all legacy admin style files and components
- Making admin-style-v3 the default and only stylesheet
This change reduces maintenance overhead and simplifies the admin styling codebase by removing the old styling system that was being conditionally loaded based on feature flags.
