feat: smart update check with auto-upgrade, snooze backoff, config CLI (v0.3.9) (#62) * feat: add bin/gstack-config CLI for reading/writing ~/.gstack/config.yaml Simple get/set/list interface for persistent gstack configuration. Used by update-check and upgrade skill for auto_upgrade and update_check settings. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com> * feat: smart update check with 12h cache, snooze backoff, config disable - Reduce cache TTL from 24h to 12h for faster update detection - Add exponential snooze backoff: 24h → 48h → 1 week (resets on new version) - Add update_check: false config option to disable checks entirely - Clear snooze file on just-upgraded - 14 new tests covering snooze levels, expiry, corruption, and config paths Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com> * feat: upgrade skill with auto-upgrade, 4-option prompt, vendored sync - Auto-upgrade mode via config or GSTACK_AUTO_UPGRADE=1 env var - 4-option AskUserQuestion: upgrade once, always, not now, never - Step 4.5: sync local vendored copy after upgrading primary install - Snooze write with escalating backoff on "Not now" - Update preamble text in gen-skill-docs for new upgrade flow - Regenerate all SKILL.md files Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com> * docs: simplify upgrade instructions, move auto-upgrade to completed README now points to /gstack-upgrade instead of long paste commands. Auto-upgrade TODO moved to Completed section (v0.3.8). Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com> * chore: bump version and changelog (v0.3.9) Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com> --------- Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>