Add omarchycn-keyring package and container build script

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01QKxGW1raAWaqeU8WdHsMsp

packages/build-keyring.sh

@@ -0,0 +1,19 @@
+#!/bin/bash
+# Builds omarchycn-keyring in a clean archlinux container; output to packages/out/
+
+set -euo pipefail
+
+ROOT=$(cd -- "$(dirname -- "${BASH_SOURCE[0]}")/.." && pwd)
+
+docker run --rm -v "$ROOT:/src:ro" -v "$ROOT/packages/out:/out" archlinux/archlinux:latest bash -c '
+set -euo pipefail
+pacman -Sy --noconfirm --quiet base-devel > /dev/null
+useradd -m builder
+cp -r /src/packages/omarchycn-keyring /home/builder/pkg
+cp /src/cn/keys/omarchycn-registry.asc /src/cn/keys/omarchycn-release.asc /home/builder/pkg/
+chown -R builder /home/builder/pkg
+cd /home/builder/pkg
+sudo -u builder makepkg --noconfirm
+install -m644 omarchycn-keyring-*.pkg.tar.zst /out/
+'
+echo "Built: $(ls "$ROOT"/packages/out/omarchycn-keyring-*.pkg.tar.zst)"