Changes based on maintainer feedback from PR #1217:
1. Add yarn install/build steps to update process
- Added yarn availability check in validateUpdatePreconditions
- Added yarn install and yarn build steps after composer install
- Added yarn rebuild to rollback process
- Updated total steps count from 12 to 14
2. Add environment variables to disable web features
- DISABLE_WEB_UPDATES: Completely disable web-based updates
- DISABLE_BACKUP_RESTORE: Disable backup restore from web UI
- Added checks in controller and template
3. Extract BackupManager service
- New service handles backup creation, listing, details, and restoration
- UpdateExecutor now delegates backup operations to BackupManager
- Cleaner separation of concerns for future reuse
4. Merge upstream/master and resolve translation conflicts
- Added Conrad info provider and generic web provider translations
- Kept Update Manager translations
