feat(notifications): admin push notifications and webhooks for user signup, plan changes, and payment issues

Co-authored-by: christianlouis <361235+christianlouis@users.noreply.github.com>

app/auth.py

@@ -151,10 +151,27 @@ def _ensure_user_profile(db: Session, user_data: dict) -> None:
         existing = db.query(UserProfile).filter(UserProfile.user_id == user_id).first()
         if existing is None:
             display_name = user_data.get("name") or user_data.get("preferred_username") or user_data.get("email")
+            email = user_data.get("email")
             profile = UserProfile(user_id=user_id, display_name=display_name)
             db.add(profile)
             db.commit()
             logger.info("Auto-created UserProfile for user_id=%s", user_id)
+            # Notify admins and fire webhook for new signup
+            try:
+                from app.utils.notification import notify_user_signup
+                from app.utils.webhook import dispatch_webhook_event
+
+                notify_user_signup(user_id, display_name=display_name, email=email)
+                dispatch_webhook_event(
+                    "user.signup",
+                    {
+                        "user_id": user_id,
+                        "display_name": display_name,
+                        "email": email,
+                    },
+                )
+            except Exception:
+                logger.exception("Failed to send signup notification/webhook for user_id=%s", user_id)
     except Exception:
         db.rollback()
         logger.exception("Failed to auto-create UserProfile for user_id=%s", user_id)