fix: healthcheck — replace GNU-wget -I flag with --spider

BusyBox wget in alpine doesn't support -I flag, healthcheck was
failing with 'unrecognized option' and Docker reported container
as unhealthy despite nginx working correctly.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Dockerfile

@@ -6,4 +6,4 @@ COPY nginx.conf /etc/nginx/nginx.conf
 EXPOSE 8080
 
 HEALTHCHECK --interval=30s --timeout=5s --retries=3 \
-    CMD wget -qO- http://127.0.0.1:8080/ -I 2>&1 | grep -q "301 Moved" || exit 1
+    CMD wget -q --spider http://127.0.0.1:8080/ || exit 1