feat: add multi-arch (amd64+arm64) Docker image builds

Add QEMU setup and platform flag to all three build jobs (Bay, Ship,
Gull) so that CI produces multi-arch manifests supporting both
linux/amd64 and linux/arm64.

This enables native deployment on Apple Silicon Macs (via OrbStack or
Docker Desktop) without Rosetta emulation, which was found to cause
shell/exec to hang due to fork/exec syscall translation issues.

Author: camera-2018

.github/workflows/cd.yml

@@ -33,6 +33,9 @@ jobs:
     steps:
       - uses: actions/checkout@v4
 
+      - name: Set up QEMU
+        uses: docker/setup-qemu-action@v3
+
       - uses: docker/setup-buildx-action@v3
 
       - name: Login to GHCR
@@ -58,6 +61,7 @@ jobs:
         uses: docker/build-push-action@v6
         with:
           context: pkgs/bay
+          platforms: linux/amd64,linux/arm64
           push: true
           tags: ${{ steps.meta.outputs.tags }}
           labels: ${{ steps.meta.outputs.labels }}
@@ -71,6 +75,9 @@ jobs:
     steps:
       - uses: actions/checkout@v4
 
+      - name: Set up QEMU
+        uses: docker/setup-qemu-action@v3
+
       - uses: docker/setup-buildx-action@v3
 
       - name: Login to GHCR
@@ -96,6 +103,7 @@ jobs:
         uses: docker/build-push-action@v6
         with:
           context: pkgs/ship
+          platforms: linux/amd64,linux/arm64
           push: true
           tags: ${{ steps.meta.outputs.tags }}
           labels: ${{ steps.meta.outputs.labels }}
@@ -109,6 +117,9 @@ jobs:
     steps:
       - uses: actions/checkout@v4
 
+      - name: Set up QEMU
+        uses: docker/setup-qemu-action@v3
+
       - uses: docker/setup-buildx-action@v3
 
       - name: Login to GHCR
@@ -134,6 +145,7 @@ jobs:
         uses: docker/build-push-action@v6
         with:
           context: pkgs/gull
+          platforms: linux/amd64,linux/arm64
           push: true
           tags: ${{ steps.meta.outputs.tags }}
           labels: ${{ steps.meta.outputs.labels }}