feat(whatsapp): add group mention detection and enhanced agent context (#81)

Merged WhatsApp group mention detection and enhanced agent context.

Features:
- Group mention detection (native @mentions, reply-to-bot, regex patterns)
- Enhanced agent context (GROUP tag, @mentioned tag, via +phone)
- Group policies (requireMention, per-group config)
- 27 new tests

Written by Cameron ◯ Letta Code

.gitignore

@@ -28,12 +28,14 @@ Thumbs.db
 # IDE
 .vscode/
 .idea/
+.claude/
 
 # Runtime files
 cron-log.jsonl
 cron-jobs.json
 lettabot-agent.json
 PERSONA.md
+CLAUDE.md
 
 # Related repos
 moltbot/