fix: disable DOCKER_BUILDKIT for plain docker builds to fix DNS resolution

.gitea/actions/docker-build/action.yml

@@ -141,9 +141,14 @@ runs:
     - name: Build image
       id: build
       shell: bash
-      env:
-        DOCKER_BUILDKIT: "1"
       run: |
+        # Disable BuildKit for plain docker builds (avoids container networking issues)
+        export DOCKER_BUILDKIT=0
+
+        if [ "${{ inputs.use-buildx }}" = "true" ]; then
+          export DOCKER_BUILDKIT=1
+        fi
+
         CACHE_FROM_FLAG=""
         if [ -n "${{ inputs.cache-from }}" ] && [ "${{ inputs.use-buildx }}" = "true" ]; then
           CACHE_FROM_FLAG="--cache-from=${{ inputs.cache-from }}"