fix(docker): correct Kong gateway port for client build arg (#4046)

The web client's NEXT_PUBLIC_SUPABASE_URL build arg pointed at port 7000,
but Kong is exposed on KONG_HTTP_PORT (8000 by default), so browser-side
Supabase calls failed in the self-hosted Docker setup.

Closes #4035

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

docker/compose.yaml

@@ -123,7 +123,7 @@ services:
       context: ..
       target: production-stage
       args:
-        NEXT_PUBLIC_SUPABASE_URL: http://${HOST_IP}:7000
+        NEXT_PUBLIC_SUPABASE_URL: http://${HOST_IP}:${KONG_HTTP_PORT:-8000}
         NEXT_PUBLIC_SUPABASE_ANON_KEY: ${ANON_KEY}
         NEXT_PUBLIC_APP_PLATFORM: web
         NEXT_PUBLIC_API_BASE_URL: http://${HOST_IP}:3000