fix: healthcheck fails with BusyBox wget that lacks --spider flag

The healthcheck used wget --spider which is not supported by BusyBox wget
that ships with nginx:alpine. This caused the healthcheck to fail with
"wget: unrecognized option: spider" even when nginx was serving correctly.

The container would be permanently marked unhealthy in:
- Docker ps output
- Docker Compose health status
- Kubernetes liveness/readiness probes
- GitHub Actions verification steps

Changed to BusyBox-compatible syntax:
- Before: wget --no-verbose --tries=1 --spider http://localhost/
- After: wget -q -O /dev/null http://localhost/

Both commands check if the server responds without downloading the body,
but the new syntax works with BusyBox's limited wget implementation.

Author: claude

Dockerfile

@@ -32,7 +32,7 @@ EXPOSE 80
 
 # Health check
 HEALTHCHECK --interval=30s --timeout=3s --start-period=5s --retries=3 \
-  CMD wget --no-verbose --tries=1 --spider http://localhost/ || exit 1
+  CMD wget -q -O /dev/null http://localhost/ || exit 1
 
 # Start nginx
 CMD ["nginx", "-g", "daemon off;"]