fix: resolve merge conflicts with origin/main (v0.4.3 + v0.4.4)

Merge origin/main which added:
- v0.4.3: /document-release skill, simplified AskUserQuestion (always ELI16),
  runtime branch detection via _BRANCH preamble variable
- v0.4.4: 60-min update check TTL, --force flag for gstack-update-check

Resolved conflicts:
- VERSION: keep 0.6.0 (our version, above 0.4.4)
- CHANGELOG: all entries preserved (0.6.0 > 0.4.4 > 0.4.3 > 0.4.2)
- TODOS.md: keep both sections (Brainstorm/Design + Document-Release)
- test/skill-validation.test.ts: include all three new skills in arrays
  (brainstorm, debug, document-release)

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

CLAUDE.md

@@ -50,6 +50,7 @@ gstack/
 ├── brainstorm/      # /brainstorm skill (Socratic design exploration)
 ├── debug/           # /debug skill (systematic root-cause debugging)
 ├── retro/           # Retrospective skill
+├── document-release/ # /document-release skill (post-ship doc updates)
 ├── setup            # One-time setup: build binary + symlink skills
 ├── SKILL.md         # Generated from SKILL.md.tmpl (don't edit directly)
 ├── SKILL.md.tmpl    # Template: edit this, run gen:skill-docs