Fix Drone API build to use iLED.slnx.

Co-authored-by: Cursor <cursoragent@cursor.com>

.drone.yml

@@ -27,8 +27,8 @@ steps:
     image: mcr.microsoft.com/dotnet/sdk:10.0
     commands:
       - cd src/backend
-      - dotnet restore iLED.sln
-      - dotnet build iLED.sln -c Release --no-restore
+      - dotnet restore iLED.slnx
+      - dotnet build iLED.slnx -c Release --no-restore
 
   - name: shop
     image: node:22-bookworm