fix: replace wget with curl in frontend healthcheck

nginx:alpine is a minimal image that does not include wget.
Install curl explicitly and use curl -f for the healthcheck.

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

flight-comparator/Dockerfile.frontend

@@ -13,7 +13,9 @@ FROM nginx:alpine
 COPY --from=builder /app/dist /usr/share/nginx/html
 COPY nginx.conf /etc/nginx/conf.d/default.conf
 
+RUN apk add --no-cache curl
+
 EXPOSE 80
 
 HEALTHCHECK --interval=30s --timeout=5s --start-period=15s --retries=3 \
-    CMD wget -qO /dev/null http://localhost/ || exit 1
+    CMD curl -f http://localhost/ || exit 1