feat: add ARM64 (aarch64) architecture support for builds and packages

Add cross-architecture build support so the project can be developed on
ARM64 (Fedora aarch64 laptop) while still producing amd64 packages for
production. All build, package, publish, and install scripts are now
architecture-aware via shared arch-helper.sh detection.

- Add scripts/arch-helper.sh for shared architecture detection
- CI builds both amd64 and arm64 in matrix strategy
- nfpm.yaml uses NFPM_ARCH env var instead of hardcoded amd64
- Build scripts support MCPCTL_TARGET_ARCH for cross-compilation
- installlocal.sh auto-detects RPM/DEB and filters by architecture
- release.sh gains --both-arches flag for dual-arch releases
- Package cleanup is arch-scoped (won't clobber other arch's packages)
- build-mcpd.sh supports --platform and --multi-arch flags
- Add pnpm scripts: rpm:build:amd64, deb:build:arm64, release:both
- Conditional rpm/dpkg-deb checks for cross-distro compatibility

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

scripts/build-mcpd.sh

@@ -1,5 +1,10 @@
 #!/bin/bash
-# Build mcpd Docker image and push to Gitea container registry
+# Build mcpd Docker image and push to Gitea container registry.
+#
+# Usage:
+#   ./build-mcpd.sh [tag]                    # Build for native arch
+#   ./build-mcpd.sh [tag] --platform linux/amd64   # Build for specific platform
+#   ./build-mcpd.sh [tag] --multi-arch       # Build for both amd64 and arm64
 set -e
 
 SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd)"
@@ -16,17 +21,60 @@ REGISTRY="10.0.0.194:3012"
 IMAGE="mcpd"
 TAG="${1:-latest}"
 
-echo "==> Building mcpd image..."
-podman build -t "$IMAGE:$TAG" -f deploy/Dockerfile.mcpd .
+# Parse optional flags
+PLATFORM=""
+MULTI_ARCH=false
+shift 2>/dev/null || true
+while [[ $# -gt 0 ]]; do
+  case "$1" in
+    --platform)
+      PLATFORM="$2"
+      shift 2
+      ;;
+    --multi-arch)
+      MULTI_ARCH=true
+      shift
+      ;;
+    *)
+      shift
+      ;;
+  esac
+done
 
-echo "==> Tagging as $REGISTRY/michal/$IMAGE:$TAG..."
-podman tag "$IMAGE:$TAG" "$REGISTRY/michal/$IMAGE:$TAG"
+if [ "$MULTI_ARCH" = true ]; then
+  echo "==> Building multi-arch mcpd image (linux/amd64 + linux/arm64)..."
+  podman build --platform linux/amd64,linux/arm64 \
+    --manifest "$IMAGE:$TAG" -f deploy/Dockerfile.mcpd .
 
-echo "==> Logging in to $REGISTRY..."
-podman login --tls-verify=false -u michal -p "$GITEA_TOKEN" "$REGISTRY"
+  echo "==> Tagging manifest as $REGISTRY/michal/$IMAGE:$TAG..."
+  podman tag "$IMAGE:$TAG" "$REGISTRY/michal/$IMAGE:$TAG"
 
-echo "==> Pushing to $REGISTRY/michal/$IMAGE:$TAG..."
-podman push --tls-verify=false "$REGISTRY/michal/$IMAGE:$TAG"
+  echo "==> Logging in to $REGISTRY..."
+  podman login --tls-verify=false -u michal -p "$GITEA_TOKEN" "$REGISTRY"
+
+  echo "==> Pushing manifest to $REGISTRY/michal/$IMAGE:$TAG..."
+  podman manifest push --tls-verify=false --all \
+    "$REGISTRY/michal/$IMAGE:$TAG" "docker://$REGISTRY/michal/$IMAGE:$TAG"
+else
+  PLATFORM_FLAG=""
+  if [ -n "$PLATFORM" ]; then
+    PLATFORM_FLAG="--platform $PLATFORM"
+    echo "==> Building mcpd image for $PLATFORM..."
+  else
+    echo "==> Building mcpd image (native arch)..."
+  fi
+
+  podman build $PLATFORM_FLAG -t "$IMAGE:$TAG" -f deploy/Dockerfile.mcpd .
+
+  echo "==> Tagging as $REGISTRY/michal/$IMAGE:$TAG..."
+  podman tag "$IMAGE:$TAG" "$REGISTRY/michal/$IMAGE:$TAG"
+
+  echo "==> Logging in to $REGISTRY..."
+  podman login --tls-verify=false -u michal -p "$GITEA_TOKEN" "$REGISTRY"
+
+  echo "==> Pushing to $REGISTRY/michal/$IMAGE:$TAG..."
+  podman push --tls-verify=false "$REGISTRY/michal/$IMAGE:$TAG"
+fi
 
 # Ensure package is linked to the repository
 source "$SCRIPT_DIR/link-package.sh"