Rework invite creation as guided flow

backend/app/routers/admin.py

@@ -122,6 +122,15 @@ def _require_recipient_email(value: object) -> str:
         detail="recipient_email is required and must be a valid email address",
     )
 
+
+def _optional_recipient_email(value: object) -> Optional[str]:
+    if value is None or (isinstance(value, str) and not value.strip()):
+        return None
+    normalized = normalize_delivery_email(value)
+    if normalized:
+        return normalized
+    raise HTTPException(status_code=400, detail="recipient_email must be a valid email address")
+
 SENSITIVE_KEYS = {
     "magent_ssl_certificate_pem",
     "magent_ssl_private_key_pem",
@@ -1927,8 +1936,10 @@ async def create_invite(payload: Dict[str, Any], current_user: Dict[str, Any] =
     role = _normalize_role_or_none(payload.get("role"))
     max_uses = _parse_optional_positive_int(payload.get("max_uses"), "max_uses")
     expires_at = _parse_optional_expires_at(payload.get("expires_at"))
-    recipient_email = _require_recipient_email(payload.get("recipient_email"))
+    recipient_email = _optional_recipient_email(payload.get("recipient_email"))
     send_email = bool(payload.get("send_email"))
+    if send_email and not recipient_email:
+        raise HTTPException(status_code=400, detail="recipient_email is required for email delivery")
     delivery_message = _normalize_optional_text(payload.get("message"))
     try:
         invite = create_signup_invite(
@@ -1998,8 +2009,10 @@ async def edit_invite(invite_id: int, payload: Dict[str, Any]) -> Dict[str, Any]
     role = _normalize_role_or_none(payload.get("role"))
     max_uses = _parse_optional_positive_int(payload.get("max_uses"), "max_uses")
     expires_at = _parse_optional_expires_at(payload.get("expires_at"))
-    recipient_email = _normalize_optional_text(payload.get("recipient_email"))
+    recipient_email = _optional_recipient_email(payload.get("recipient_email"))
     send_email = bool(payload.get("send_email"))
+    if send_email and not recipient_email:
+        raise HTTPException(status_code=400, detail="recipient_email is required for email delivery")
     delivery_message = _normalize_optional_text(payload.get("message"))
     try:
         invite = update_signup_invite(