feat(discovery): trending sort heuristic over world_visits with decay weighting

backend/app/routers/discovery.py

@@ -16,6 +16,8 @@ from app.database import get_db
 from app.dependencies import OptionalUser
 from app.models.world import World, WorldVisibility
 from app.models.world_visit import WorldVisit
+from app.services.trending import get_trending_subquery
+
 
 router = APIRouter()
 
@@ -208,11 +210,23 @@ async def list_discovery_worlds(
     total = (await db.execute(count_query)).scalar_one()
 
     # Sort
-    if sort == "most_played":
+    if sort == "trending":
+        trending_subq = get_trending_subquery()
+        base_query = (
+            base_query
+            .outerjoin(trending_subq, World.id == trending_subq.c.trending_world_id)
+            .order_by(
+                func.coalesce(trending_subq.c.trending_score, 0.0).desc(),
+                World.play_count.desc(),
+                World.created_at.desc(),
+            )
+        )
+    elif sort == "most_played":
         base_query = base_query.order_by(World.play_count.desc(), World.created_at.desc())
     else:  # default: newest
         base_query = base_query.order_by(World.created_at.desc())
 
+
     # Pagination & load owner
     query = (
         base_query