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.

app/config/settings.py

@@ -32,7 +32,10 @@ class Settings(BaseSettings):
     smtp_port: int = 1025
     smtp_username: str = ""
     smtp_password: str = ""
+    email_provider: str = "log"
     smtp_use_tls: bool = False
+    smtp_use_ssl: bool = False
+    smtp_timeout_seconds: float = 10.0
     smtp_from_email: str = "no-reply@benyamessenger.local"
 
     login_rate_limit_per_minute: int = 10