feat: add myblog blog writer skill

.codex/skills/myblog-blog-writer/scripts/install_global.sh

@@ -0,0 +1,16 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+skill_dir="$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd)"
+target_dir="${CODEX_HOME:-$HOME/.codex}/skills"
+target="${target_dir}/myblog-blog-writer"
+
+mkdir -p "${target_dir}"
+
+if [[ -e "${target}" && ! -L "${target}" ]]; then
+  echo "Refusing to replace existing non-symlink: ${target}" >&2
+  exit 1
+fi
+
+ln -sfn "${skill_dir}" "${target}"
+echo "Linked ${target} -> ${skill_dir}"