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/release.sh

@@ -1,4 +1,9 @@
 #!/bin/bash
+# Build, publish, and install mcpctl packages.
+#
+# Usage:
+#   ./release.sh               # Build + publish for native arch only
+#   ./release.sh --both-arches # Build + publish for both amd64 and arm64
 set -e
 
 SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd)"
@@ -10,24 +15,47 @@ if [ -f .env ]; then
   set -a; source .env; set +a
 fi
 
+source "$SCRIPT_DIR/arch-helper.sh"
+resolve_arch "${MCPCTL_TARGET_ARCH:-}"
+NATIVE_ARCH="$NFPM_ARCH"
+
+BOTH_ARCHES=false
+if [[ "${1:-}" == "--both-arches" ]]; then
+  BOTH_ARCHES=true
+fi
+
 echo "=== mcpctl release ==="
+echo "    Native arch: $NATIVE_ARCH"
 echo ""
 
-# Build
-bash scripts/build-rpm.sh
+build_and_publish() {
+  local arch="$1"
+  echo ""
+  echo "=== Building for $arch ==="
+  MCPCTL_TARGET_ARCH="$arch" bash scripts/build-rpm.sh
+  echo ""
+  MCPCTL_TARGET_ARCH="$arch" bash scripts/publish-rpm.sh
+  MCPCTL_TARGET_ARCH="$arch" bash scripts/publish-deb.sh
+}
+
+if [ "$BOTH_ARCHES" = true ]; then
+  build_and_publish "amd64"
+  build_and_publish "arm64"
+else
+  build_and_publish "$NATIVE_ARCH"
+fi
 
 echo ""
 
-# Publish
-bash scripts/publish-rpm.sh
-bash scripts/publish-deb.sh
-
-echo ""
-
-# Install locally
-echo "==> Installing locally..."
-RPM_FILE=$(ls dist/mcpctl-*.rpm 2>/dev/null | head -1)
-sudo rpm -U --force "$RPM_FILE"
+# Install locally for native arch (auto-detect RPM or DEB)
+echo "==> Installing locally (${NATIVE_ARCH})..."
+if command -v dpkg &>/dev/null && ! command -v dnf &>/dev/null; then
+  DEB_FILE=$(ls dist/mcpctl*.deb 2>/dev/null | grep -E "[._]${NATIVE_ARCH}[._]" | head -1)
+  sudo dpkg -i "$DEB_FILE" || sudo apt-get install -f -y
+else
+  RPM_FILE=$(ls dist/mcpctl-*.rpm 2>/dev/null | grep -E "[._]${NATIVE_ARCH}[._]" | head -1)
+  sudo rpm -U --force "$RPM_FILE"
+fi
 
 echo ""
 echo "==> Installed:"