* chore: remove legacy mapping + admin profiles section, page user mappings
- Delete the hardcoded github_user_email_map.py and the one-time
POST /admin/user-mappings/import endpoint + Import legacy mapping UI
button (the Store is now the sole source of truth post-import).
- Remove the per-user profiles admin section and its GET/PUT
/admin/profiles endpoints + ProfileForm component; users still manage
their own profile via My Settings.
- Page the user mappings list: /admin/user-mappings now takes
page/page_size and returns {items,total,page,page_size}; the admin UI
shows 20 rows per page with Previous/Next controls.
* Address review: fix stale import-button doc + clamp mappings page on shrink
c41185a3ca