fix(review): remove dead code, fix gitignore pattern, correct changelog

- Remove unused getSenderWindow() from autoUpdateBridge (replaced by broadcastToAllWindows)
- Fix .gitignore: /CLAUDE.md instead of CLAUDE.md to only match root
- Merge duplicate [Unreleased] sections in CHANGELOG.md
- Correct checkNow description: uses GitHub API, then triggers electron-updater async

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

.gitignore

@@ -37,7 +37,7 @@ coverage
 
 # Claude Code local settings
 /.claude/settings.local.json
-CLAUDE.md
+/CLAUDE.md
 
 # AI / Superpowers generated docs (local only)
 /docs/superpowers/