ci: fix Java 21 in dockerfile, add Docker Hub login to avoid rate limits

.gitea/workflows/build.yml

@@ -22,7 +22,14 @@ jobs:
       - name: Set up Docker Buildx
         uses: docker/setup-buildx-action@v3
 
-      # 5. Docker login
+      # 5. Login to Docker Hub to avoid pull rate limits
+      - name: Login to Docker Hub
+        uses: docker/login-action@v3
+        with:
+          username: ${{ secrets.DOCKERHUB_USER }}
+          password: ${{ secrets.DOCKERHUB_TOKEN }}
+
+      # 6. Docker login to Gitea registry
       - name: Login to Docker Registry
         uses: docker/login-action@v3
         with:
@@ -30,7 +37,7 @@ jobs:
           username: ${{ secrets.TEAUSER }}
           password: ${{ secrets.TEAPASSWORD }}
 
-      # 6. Build and push Docker image with layer caching
+      # 7. Build and push Docker image with layer caching
       - name: Build and Push Docker Image
         uses: docker/build-push-action@v5
         with:
@@ -40,7 +47,7 @@ jobs:
           cache-from: type=registry,ref=tea.zendric.de/cedric/xpensely-server:buildcache
           cache-to: type=registry,ref=tea.zendric.de/cedric/xpensely-server:buildcache,mode=max
 
-      # 7. Trigger Dokploy to redeploy the dev server automatically
+      # 8. Trigger Dokploy to redeploy the dev server automatically
       - name: Trigger Dokploy Redeploy
         run: |
           curl -X POST "${{ secrets.DOKPLOY_WEBHOOK_URL }}" \