feat: add maintenance slash commands for release management

Commands added:
- /update-infos-release [bump-type]: Automate CC releases tracking + version bump
- /version: Display guide & CC versions with content stats
- /changelog [count]: View recent CHANGELOG entries
- /sync: Check guide/landing synchronization status

Workflow automation:
- Claude Code releases tracking (YAML + MD + Landing badge)
- Guide version management (VERSION + sync all docs)
- CHANGELOG updates
- Landing site sync verification
- Git commit/push to both repositories

Files:
- .claude/commands/update-infos-release.md: Full release workflow
- .claude/commands/version.md: Version info display
- .claude/commands/changelog.md: CHANGELOG viewer
- .claude/commands/sync.md: Sync check with actionable fixes
- .gitignore: Allow .claude/commands/ while ignoring other .claude/ config
- CLAUDE.md: Document new maintenance commands

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

.gitignore

@@ -5,8 +5,9 @@
 *.swo
 *~
 
-# Claude Code
+# Claude Code (ignore personal config, but keep shared commands)
 .claude/
+!.claude/commands/
 
 # OS
 .DS_Store