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/campaigns/infrastructure/http/dto.rs

@@ -0,0 +1,22 @@
+use chrono::{DateTime, Utc};
+use serde::{Deserialize, Serialize};
+use utoipa::ToSchema;
+use uuid::Uuid;
+
+#[derive(Debug, Deserialize, ToSchema)]
+pub struct CreateCampaignRequest {
+    pub name: String,
+    pub url: String,
+}
+
+#[derive(Debug, Serialize, ToSchema)]
+pub struct CampaignResponse {
+    pub id: Uuid,
+    pub name: String,
+    pub url: String,
+    pub is_active: bool,
+    pub created_by: Uuid,
+    pub expires_at: DateTime<Utc>,
+    pub created_at: Option<DateTime<Utc>>,
+    pub updated_at: Option<DateTime<Utc>>,
+}