feat(whatsapp): add lettabot-message CLI support for text and files (#89)

Merged WhatsApp CLI support with HTTP API server.

Features:
- HTTP API server for CLI-to-bot communication across Docker boundaries
- WhatsApp text + file sending via `lettabot-message send --file photo.jpg`
- Unified multipart endpoint at /api/v1/messages
- Security: timing-safe auth, localhost binding, same-origin CORS
- Bad MAC error handling for WhatsApp encryption renegotiation

Written by Cameron ◯ Letta Code

.gitignore

@@ -34,6 +34,7 @@ Thumbs.db
 cron-log.jsonl
 cron-jobs.json
 lettabot-agent.json
+lettabot-api.json
 PERSONA.md
 CLAUDE.md