feat(profile): add round avatar with upload and cropping

- backend: user_avatar_objects binding (PG+SQLite), GC preserves avatar blobs,
  avatar service (EXIF-stripping WebP 128/512), public avatar read route
- web: avatar upload/crop on profile, round avatar in header/members/comments/author
- android: avatar upload/crop, round avatar on profile and albums header
- openspec: add-user-avatar proposal/design/specs/tasks

README.md

@@ -308,6 +308,8 @@ deploy/                  # systemd unit, пример nginx
   (`identifier` — email или E.164-телефон), `POST /api/auth/refresh|logout`
 - `GET|PATCH|DELETE /api/auth/me`, `POST /api/auth/me/password`,
   `POST /api/auth/me/identifiers`, `PATCH /api/auth/me/preferences`
+- `POST|DELETE /api/auth/me/avatar` (круглый аватар: загрузка готового квадрата),
+  `GET /api/avatars/:userID/:version?size=large` (публичная отдача аватара)
 - `GET|POST /api/albums`, `GET|PATCH|DELETE /api/albums/:id`
 - `GET /api/albums/:id/members`, `POST /api/albums/:id/invites`,
   `POST /api/invites/:token/accept`, `PATCH|DELETE /api/albums/:id/members/:user_id`