feat: migrate imphnen-backend-qr into workspace as imphnen-qr crate

Ports the Go QR campaign overlay service to a self-contained Rust crate
nested at /v1/qr/... in the gateway.

Features:
- Auth: register, login, Google OAuth, JWT refresh (bcrypt compat with Go DB)
- Users: profile management + admin CRUD (list/role/delete)
- Campaigns: create (auto-generates QR PNG via qrcode crate), list,
  activate, delete; process-image endpoint overlays active campaign QR
  onto uploaded images (bottom-right corner, image crate)
- QR pool connects to imphnen_qr database via QR_DATABASE_URL

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

imphnen-qr/src/users/mod.rs

@@ -0,0 +1,4 @@
+pub mod domain;
+pub mod application;
+pub mod infrastructure;
+pub use infrastructure::http::routes::qr_users_routes;