When switching storage drivers in admin settings, save now validates
connectivity against the selected target backend instead of retesting
the still-active driver. The active driver remains unchanged until
migration completes, so unreachable MinIO no longer blocks saving local
storage settings.
Move route-specific admin components from components/common/admin into
app/(main)/admin/<feature>/components/. Split AdminService god object into
domain services, fix UploadService to use BaseService, add AdminUploadService,
consolidate DB export into DbManageService, and migrate consumers to the
unified services entry.
ryan