Fix health check 404: add /api/health route, remove nginx /health proxy

Frontend API_BASE is /api in production, so health check was hitting
/api/health which didn't exist. Added /api/health on the server and
removed the now-unnecessary separate nginx /health proxy rule.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

apps/web/nginx.conf

@@ -10,10 +10,6 @@ server {
         proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
     }
 
-    location /health {
-        proxy_pass http://server:3001;
-    }
-
     location / {
         try_files $uri $uri/ /index.html;
     }