fix: health check false-negative + add rollback on failure

The deploy pipeline had two critical bugs:

1. Health check used /api/vehicles/ZZZ999 with curl -f. This endpoint
   returns HTTP 404 for unknown plates (correct behavior), which curl -f
   treated as a failure. The backend was actually healthy.
   Fix: use /api/vehicles/ABC123 (seeded in V6 migration, always 200)
   and remove -f flag from curl.

2. No rollback on failure. If health checks failed, containers stayed
   running forever because the pipeline exited 1 without stopping them.
   Fix: combine health checks into one step. If either fails, run
   'docker compose down' (without -v, so DB volume is preserved) before
   exiting with failure.

.forgejo/workflows/deploy.yml

@@ -45,36 +45,46 @@ jobs:
           docker compose -p bilhej-prod -f docker-compose.prod.yml down
           docker compose -p bilhej-prod -f docker-compose.prod.yml up --build -d
 
-      - name: Wait for services
-        run: sleep 20
-
-      - name: Health check — backend API
+      - name: Health checks with rollback
         run: |
+          echo "Waiting for services to start..."
+          sleep 20
+
+          BACKEND_OK=false
           for i in 1 2 3 4 5; do
             if docker run --rm --network bilhej-prod_default curlimages/curl:8.5.0 \
-               -sf http://bilhej-backend-prod:8080/api/vehicles/ZZZ999; then
+               -s http://bilhej-backend-prod:8080/api/vehicles/ABC123 > /dev/null; then
               echo "Backend is healthy"
-              exit 0
+              BACKEND_OK=true
+              break
             fi
-            echo "Attempt $i failed, retrying in 5s..."
+            echo "Backend check attempt $i failed, retrying in 5s..."
             sleep 5
           done
-          echo "Backend health check failed"
-          exit 1
 
-      - name: Health check — frontend
-        run: |
+          FRONTEND_OK=false
           for i in 1 2 3 4 5; do
             if docker run --rm --network bilhej-prod_default curlimages/curl:8.5.0 \
-               -sf http://bilhej-frontend-prod/ | grep -qi "bilhej\|Bilhej\|BilHej"; then
+               -s http://bilhej-frontend-prod/ | grep -qi "bilhej\|Bilhej\|BilHej"; then
               echo "Frontend is serving"
-              exit 0
+              FRONTEND_OK=true
+              break
             fi
-            echo "Attempt $i failed, retrying in 5s..."
+            echo "Frontend check attempt $i failed, retrying in 5s..."
             sleep 5
           done
-          echo "Frontend health check failed"
-          exit 1
+
+          if [ "$BACKEND_OK" != "true" ] || [ "$FRONTEND_OK" != "true" ]; then
+            echo ""
+            echo "═══════════════════════════════════════════════════"
+            echo "  HEALTH CHECK FAILED — ROLLING BACK DEPLOYMENT"
+            echo "═══════════════════════════════════════════════════"
+            echo ""
+            docker compose -p bilhej-prod -f docker-compose.prod.yml down
+            echo ""
+            echo "Rolled back. Containers stopped. DB volume preserved."
+            exit 1
+          fi
 
       - name: Print deploy status
         run: |