fix: resolve MMDL hairpinning issue with CalDAV communication

- Add cal.thesatelliteoflove.com:172.20.0.5 to MMDL extra_hosts for internal communication
- Update DEPLOYMENT_LEARNINGS.md with comprehensive hairpinning documentation
- Update CLAUDE.md with hairpinning guidance and correct deployment commands
- Document standard pattern for Docker container internal domain resolution

🤖 Generated with [Claude Code](https://claude.ai/code)

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

roles/docker/templates/mmdl-compose.yml.j2

@@ -10,6 +10,7 @@ services:
     extra_hosts:
       - "host.docker.internal:host-gateway"
       - "auth.thesatelliteoflove.com:172.20.0.5"
+      - "cal.thesatelliteoflove.com:172.20.0.5"
     labels:
       glance.name: MMDL
       glance.icon: si:task