feat: multi-architecture builds (x86_64 + arm64)

- build-rpm.sh: --arch flag for targeting x86_64 or arm64, --all for both
  Uses bun cross-compile with --target=bun-linux-x64/arm64
- build-bastion.sh: --arch flag for Docker platform targeting
- release.sh: builds both architectures by default
- CI: builds + publishes RPM/DEB for both architectures

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

bastion/scripts/build-bastion.sh

@@ -11,14 +11,72 @@ if [ -f .env ]; then
   set -a; source .env; set +a
 fi
 
+# ── Argument parsing ───────────────────────────────────────────────
+TARGET_ARCH=""
+
+usage() {
+  cat <<EOF
+Usage: $(basename "$0") [OPTIONS] [TAG]
+
+Build bastion container image and optionally push to registry.
+
+Options:
+  --arch ARCH    Target platform: x86_64 or arm64 (default: host arch)
+  -h, --help     Show this help message
+
+Arguments:
+  TAG            Image tag (default: version from package.json)
+EOF
+  exit 0
+}
+
+POSITIONAL_ARGS=()
+while [[ $# -gt 0 ]]; do
+  case "$1" in
+    --arch)
+      TARGET_ARCH="$2"
+      shift 2
+      ;;
+    -h|--help)
+      usage
+      ;;
+    *)
+      POSITIONAL_ARGS+=("$1")
+      shift
+      ;;
+  esac
+done
+
 # Registry defaults to internal address (external proxy has body size limit)
 REGISTRY="${GITEA_REGISTRY:-mysources.co.uk}"
 IMAGE="lab-bastion"
 VERSION=$(node -p "require('./package.json').version")
-TAG="${1:-$VERSION}"
+TAG="${POSITIONAL_ARGS[0]:-$VERSION}"
 
-echo "==> Building bastion image (tag: $TAG)..."
-podman build -t "$IMAGE:$TAG" -f stack/Dockerfile .
+# ── Resolve target platform ───────────────────────────────────────
+detect_host_arch() {
+  local machine
+  machine="$(uname -m)"
+  case "$machine" in
+    x86_64)  echo "x86_64" ;;
+    aarch64) echo "arm64" ;;
+    arm64)   echo "arm64" ;;
+    *)       echo "$machine" ;;
+  esac
+}
+
+docker_platform_for() {
+  case "$1" in
+    x86_64) echo "linux/amd64" ;;
+    arm64)  echo "linux/arm64" ;;
+  esac
+}
+
+ARCH="${TARGET_ARCH:-$(detect_host_arch)}"
+PLATFORM="$(docker_platform_for "$ARCH")"
+
+echo "==> Building bastion image (tag: $TAG, platform: $PLATFORM)..."
+podman build --platform "$PLATFORM" -t "$IMAGE:$TAG" -f stack/Dockerfile .
 
 echo "==> Tagging as $REGISTRY/michal/$IMAGE:$TAG..."
 podman tag "$IMAGE:$TAG" "$REGISTRY/michal/$IMAGE:$TAG"
@@ -41,3 +99,4 @@ fi
 
 echo "==> Done!"
 echo "    Image: $REGISTRY/michal/$IMAGE:$TAG"
+echo "    Platform: $PLATFORM"