Implement real SMTP delivery and transactional email auth flow

Email delivery:

- Replaced logging-only email sender with aiosmtplib SMTP implementation.

- Added provider mode switch via EMAIL_PROVIDER (log/smtp).

- Added TLS/SSL and timeout controls for SMTP transport.

Auth registration flow:

- Made register/resend/reset email flows transactional with rollback on delivery failure.

- Return 503 when verification/reset email cannot be delivered.

Configuration:

- Extended settings and env templates for EMAIL_PROVIDER, SMTP_USE_SSL, SMTP_TIMEOUT_SECONDS.

- Updated docker-compose environment mapping for new SMTP variables.

docker-compose.yml

@@ -24,7 +24,10 @@ x-app-env: &app-env
   SMTP_PORT: ${SMTP_PORT:-1025}
   SMTP_USERNAME: ${SMTP_USERNAME:-}
   SMTP_PASSWORD: ${SMTP_PASSWORD:-}
+  EMAIL_PROVIDER: ${EMAIL_PROVIDER:-log}
   SMTP_USE_TLS: ${SMTP_USE_TLS:-false}
+  SMTP_USE_SSL: ${SMTP_USE_SSL:-false}
+  SMTP_TIMEOUT_SECONDS: ${SMTP_TIMEOUT_SECONDS:-10}
   SMTP_FROM_EMAIL: ${SMTP_FROM_EMAIL:-no-reply@benyamessenger.local}
   LOGIN_RATE_LIMIT_PER_MINUTE: ${LOGIN_RATE_LIMIT_PER_MINUTE:-10}
   REGISTER_RATE_LIMIT_PER_MINUTE: ${REGISTER_RATE_LIMIT_PER_MINUTE:-5}