feat(infrastructure): use celery worker

backend/app/workers/celery_tasks.py

@@ -0,0 +1,44 @@
+import logging
+from typing import Any, Dict
+
+from celery import shared_task
+
+logger = logging.getLogger("celery_tasks")
+if not logger.handlers:
+    _h = logging.StreamHandler()
+    logger.addHandler(_h)
+logger.setLevel(logging.INFO)
+
+
+@shared_task(name="workers.send_email")
+def send_email(payload: Dict[str, Any]) -> None:
+    """Celery task to send an email.
+
+    Expected payload schema:
+    {
+        "type": "email",
+        "to": "recipient@example.com",
+        "subject": "Subject text",
+        "body": "Email body text"
+    }
+
+    This mirrors the previous queue worker contract to minimize changes upstream.
+    """
+    to = payload.get("to")
+    subject = payload.get("subject")
+    body = payload.get("body")
+    if not (to and subject and body):
+        logger.error("Email task missing fields. Payload: %s", payload)
+        return
+
+    # Placeholder for real email sending logic
+    # Implement SMTP provider call here
+    logger.info("[Celery] Email sent | to=%s | subject=%s | body_len=%d", to, subject, len(body))
+
+
+@shared_task(name="workers.send_email_fields")
+def send_email_fields(to: str, subject: str, body: str) -> None:
+    """Alternate signature for convenience when calling from app code.
+    Routes to the same implementation as send_email.
+    """
+    send_email({"type": "email", "to": to, "subject": subject, "body": body})