Add email password change feature and fix nginx config

- Add public page at /email/change-password for Poste.io mailbox password management
- Add API routes for SMTP credential verification and Poste.io password change
- Rewrite nginx config as HTTP-only (certbot --nginx will add SSL)
- Add Poste.io admin API env vars to docker-compose and env templates

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

docker/docker-compose.yml

@@ -33,6 +33,10 @@ services:
       - SMTP_USER=${SMTP_USER}
       - SMTP_PASS=${SMTP_PASS}
       - EMAIL_FROM=${EMAIL_FROM}
+      - POSTE_API_URL=${POSTE_API_URL:-https://mail.monaco-opc.com}
+      - POSTE_ADMIN_EMAIL=${POSTE_ADMIN_EMAIL}
+      - POSTE_ADMIN_PASSWORD=${POSTE_ADMIN_PASSWORD}
+      - POSTE_MAIL_DOMAIN=${POSTE_MAIL_DOMAIN:-monaco-opc.com}
       - OPENAI_API_KEY=${OPENAI_API_KEY:-}
       - OPENAI_MODEL=${OPENAI_MODEL:-gpt-4o}
       - MAX_FILE_SIZE=${MAX_FILE_SIZE:-524288000}