Fix: Load user relationship in listings API to prevent 500 error

backend/app/api/listings.py

@@ -27,6 +27,7 @@ from fastapi import APIRouter, Depends, Query, HTTPException, Request
 from pydantic import BaseModel, Field, EmailStr
 from sqlalchemy import select, func, and_
 from sqlalchemy.ext.asyncio import AsyncSession
+from sqlalchemy.orm import selectinload
 
 from app.database import get_db
 from app.api.deps import get_current_user, get_current_user_optional
@@ -284,7 +285,7 @@ async def browse_listings(
     db: AsyncSession = Depends(get_db),
 ):
     """Browse active domain listings (public)."""
-    query = select(DomainListing).where(
+    query = select(DomainListing).options(selectinload(DomainListing.user)).where(
         DomainListing.status == ListingStatus.ACTIVE.value
     )
     
@@ -413,7 +414,9 @@ async def get_listing_by_slug(
 ):
     """Get listing details by slug (public)."""
     result = await db.execute(
-        select(DomainListing).where(
+        select(DomainListing)
+        .options(selectinload(DomainListing.user))
+        .where(
             and_(
                 DomainListing.slug == slug,
                 DomainListing.status == ListingStatus.ACTIVE.value,