fix(traefik): Route tenant subdomains to nginx instead of django

The subdomain-router was incorrectly sending tenant subdomain requests
directly to Django (API server), causing 404 errors. Now routes to nginx
which serves the React SPA and proxies /api/ requests to Django.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

smoothschedule/compose/production/traefik/traefik.yml

@@ -87,13 +87,14 @@ http:
 
     # Wildcard subdomain router for tenant subdomains
     # Each subdomain gets its own certificate via HTTP challenge
+    # Routes to nginx which serves the frontend SPA and proxies /api/ to Django
     subdomain-router:
       rule: 'HostRegexp(`{subdomain:[a-z0-9-]+}.smoothschedule.com`)'
       entryPoints:
         - web-secure
       middlewares:
         - csrf
-      service: django
+      service: nginx
       tls:
         certResolver: letsencrypt