Migrate build assets and scripts to deploy/docker structure

- Removed `install.sh` and moved Docker-related assets to `deploy/docker`.
- Updated all Dockerfile references from `build/` to `deploy/docker/`.
- Refactored paths in E2E tests, Makefile, and documentation for consistency with new directory structure.
- Added `HAPROXY_STATS_CORS_ORIGIN` environment variable in `docker-compose.yml`.

deploy/docker/assets/entrypoint.sh

@@ -0,0 +1,13 @@
+#!/bin/sh
+set -e
+
+## When docker.sock is mounted its GID comes from the host and is unknown at
+## build time. Detect it at startup and add the haproxy user to that group so
+## Docker/Swarm discovery works without running the whole process as root.
+#if [ -S /var/run/docker.sock ]; then
+#    SOCK_GID=$(stat -c '%g' /var/run/docker.sock)
+#    getent group "$SOCK_GID" >/dev/null 2>&1 || addgroup -g "$SOCK_GID" dockersock
+#    addgroup haproxy "$(getent group "$SOCK_GID" | cut -d: -f1)" 2>/dev/null || true
+#fi
+
+exec /scripts/.venv/bin/easy-haproxy "$@"