ci: remove arm64 build + QEMU — amd64 only

Removes linux/arm64 from multi-platform build and drops QEMU setup.
All infra (prod + staging) is x86. QEMU emulation was adding ~12min
to every CI run for an unused architecture.

.github/workflows/deploy.yml

@@ -275,10 +275,6 @@ jobs:
           docker compose -f "$STAGING_COMPOSE_FILE" -p corescope-staging build "$STAGING_SERVICE"
           echo "Built Go staging image ✅"
 
-      - name: Set up QEMU
-        if: github.event_name == 'push'
-        uses: docker/setup-qemu-action@v3
-
       - name: Set up Docker Buildx
         if: github.event_name == 'push'
         uses: docker/setup-buildx-action@v3
@@ -310,7 +306,7 @@ jobs:
         with:
           context: .
           push: true
-          platforms: linux/amd64,linux/arm64
+          platforms: linux/amd64
           tags: ${{ steps.docker-meta.outputs.tags }}
           labels: ${{ steps.docker-meta.outputs.labels }}
           build-args: |