fix: add linux/arm64 support to Docker image builds

Add QEMU emulation and multi-platform build config so ARM64 users
can pull the image without "no matching manifest" errors.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.github/workflows/bump.yml

@@ -70,6 +70,9 @@ jobs:
             type=semver,pattern={{major}}.{{minor}},value=${{ needs.bump.outputs.tag }}
             type=raw,value=latest
 
+      - name: Set up QEMU (for multi-platform builds)
+        uses: docker/setup-qemu-action@v3
+
       - name: Set up Docker Buildx
         uses: docker/setup-buildx-action@v3
 
@@ -84,6 +87,7 @@ jobs:
         uses: docker/build-push-action@v6
         with:
           context: .
+          platforms: linux/amd64,linux/arm64
           push: true
           tags: ${{ steps.meta.outputs.tags }}
           labels: ${{ steps.meta.outputs.labels }}

.github/workflows/release.yml

@@ -30,6 +30,9 @@ jobs:
             type=semver,pattern={{major}}.{{minor}}
             type=raw,value=latest
 
+      - name: Set up QEMU (for multi-platform builds)
+        uses: docker/setup-qemu-action@v3
+
       - name: Set up Docker Buildx
         uses: docker/setup-buildx-action@v3
 
@@ -44,6 +47,7 @@ jobs:
         uses: docker/build-push-action@v6
         with:
           context: .
+          platforms: linux/amd64,linux/arm64
           push: true
           tags: ${{ steps.meta.outputs.tags }}
           labels: ${{ steps.meta.outputs.labels }}