feat(infra): configure imgproxy to use next.js rewrite proxy

- Added /_img/ rewrite rule in next.config.mjs to proxy image requests to IMGPROXY_URL
- Updated lib/imgproxy.ts to use local /_img path instead of exposed public URL
- Replaced NEXT_PUBLIC_IMGPROXY_URL (build-time) with IMGPROXY_URL (runtime)
- Updated Dockerfile and docker-compose.yml to strip unused build args

scripts/audit-local.sh

@@ -9,7 +9,7 @@ echo "🚀 Starting High-Fidelity Local Audit..."
 
 # 1. Environment and Infrastructure
 export DOCKER_HOST="unix:///Users/marcmintel/.docker/run/docker.sock"
-export NEXT_PUBLIC_IMGPROXY_URL="http://img.klz.localhost"
+export IMGPROXY_URL="http://img.klz.localhost"
 export NEXT_URL="http://klz.localhost"
 
 docker network create infra 2>/dev/null || true