Remove QEMU, build linux/arm64 natively on ARM runner; v2.0.48

Runner is on the ARM server so linux/arm64 builds natively — no QEMU
or cross-compilation needed. Drop setup-qemu-action and amd64 platform.

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

.gitea/workflows/docker-publish.yml

@@ -17,9 +17,6 @@ jobs:
       - name: Checkout
         uses: actions/checkout@v4
 
-      - name: Set up QEMU
-        uses: docker/setup-qemu-action@v3
-
       - name: Set up Docker Buildx
         uses: docker/setup-buildx-action@v3
 
@@ -56,7 +53,7 @@ jobs:
         with:
           context: .
           push: true
-          platforms: linux/amd64,linux/arm64
+          platforms: linux/arm64
           tags: ${{ steps.meta.outputs.tags }}
           labels: ${{ steps.meta.outputs.labels }}
           build-args: |