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/email/service.py

@@ -1,22 +1,74 @@
 import logging
+from email.message import EmailMessage
+
+import aiosmtplib
 
 from app.config.settings import settings
 
 logger = logging.getLogger(__name__)
 
 
+class EmailDeliveryError(Exception):
+    pass
+
+
 class EmailService:
     async def send_verification_email(self, email: str, token: str) -> None:
         verify_link = f"{settings.frontend_base_url}/verify-email?token={token}"
         subject = "Verify your BenyaMessenger account"
-        body = f"Open this link to verify your account: {verify_link}"
-        logger.info("EMAIL to=%s subject=%s body=%s", email, subject, body)
+        text = (
+            "Welcome to BenyaMessenger.\n\n"
+            f"Verify your email by opening this link:\n{verify_link}\n\n"
+            "If you did not create this account, ignore this email."
+        )
+        html = (
+            "<p>Welcome to <b>BenyaMessenger</b>.</p>"
+            f"<p>Verify your email by opening this link:<br><a href='{verify_link}'>{verify_link}</a></p>"
+            "<p>If you did not create this account, ignore this email.</p>"
+        )
+        await self._send_email(email, subject, text, html)
 
     async def send_password_reset_email(self, email: str, token: str) -> None:
         reset_link = f"{settings.frontend_base_url}/reset-password?token={token}"
         subject = "Reset your BenyaMessenger password"
-        body = f"Open this link to reset your password: {reset_link}"
-        logger.info("EMAIL to=%s subject=%s body=%s", email, subject, body)
+        text = (
+            "Password reset request.\n\n"
+            f"Open this link to reset your password:\n{reset_link}\n\n"
+            "If you did not request this, ignore this email."
+        )
+        html = (
+            "<p>Password reset request.</p>"
+            f"<p>Open this link to reset your password:<br><a href='{reset_link}'>{reset_link}</a></p>"
+            "<p>If you did not request this, ignore this email.</p>"
+        )
+        await self._send_email(email, subject, text, html)
+
+    async def _send_email(self, recipient: str, subject: str, text: str, html: str) -> None:
+        if settings.email_provider.lower() != "smtp":
+            logger.info("EMAIL to=%s subject=%s body=%s", recipient, subject, text)
+            return
+
+        message = EmailMessage()
+        message["From"] = settings.smtp_from_email
+        message["To"] = recipient
+        message["Subject"] = subject
+        message.set_content(text)
+        message.add_alternative(html, subtype="html")
+
+        try:
+            await aiosmtplib.send(
+                message,
+                hostname=settings.smtp_host,
+                port=settings.smtp_port,
+                username=settings.smtp_username or None,
+                password=settings.smtp_password or None,
+                start_tls=settings.smtp_use_tls,
+                use_tls=settings.smtp_use_ssl,
+                timeout=settings.smtp_timeout_seconds,
+            )
+        except Exception as exc:
+            logger.exception("SMTP delivery failed to=%s subject=%s", recipient, subject)
+            raise EmailDeliveryError("Email delivery failed") from exc
 
 
 def get_email_service() -> EmailService: