fix: enforce Codex 1024-char description limit + auto-heal stale installs (v0.11.9.0) (#391)

* fix: enforce 1024-char Codex description limit + auto-heal stale installs

Build-time guard in gen-skill-docs.ts throws if any Codex description
exceeds 1024 chars. Setup always regenerates .agents/ to prevent stale
files. One-time migration in gstack-update-check deletes oversized
SKILL.md files so they get regenerated on next setup/upgrade.

* chore: bump version and changelog (v0.11.9.0)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

README.md

@@ -224,6 +224,8 @@ Data is stored in [Supabase](https://supabase.com) (open source Firebase alterna
 
 **Stale install?** Run `/gstack-upgrade` — or set `auto_upgrade: true` in `~/.gstack/config.yaml`
 
+**Codex says "Skipped loading skill(s) due to invalid SKILL.md"?** Your Codex skill descriptions are stale. Fix: `cd ~/.codex/skills/gstack && git pull && ./setup --host codex` — or for repo-local installs: `cd "$(readlink -f .agents/skills/gstack)" && git pull && ./setup --host codex`
+
 **Windows users:** gstack works on Windows 11 via Git Bash or WSL. Node.js is required in addition to Bun — Bun has a known bug with Playwright's pipe transport on Windows ([bun#4253](https://github.com/oven-sh/bun/issues/4253)). The browse server automatically falls back to Node.js. Make sure both `bun` and `node` are on your PATH.
 
 **Claude says it can't see the skills?** Make sure your project's `CLAUDE.md` has a gstack section. Add this: