Add multi-site Caddy helpers and document usage

- add startup/shutdown scripts that render a Caddyfile from JSON config and run health checks

- add Python utilities and a sample sites.json for declarative multi-site configuration

- document the workflow and ignore generated Caddy state artifacts

- normalize double-quote style across challenge workflow controllers, nodes, and tests

docker/caddy/load_metadata.py

@@ -0,0 +1,29 @@
+"""Load site metadata without rewriting the Caddyfile."""
+from __future__ import annotations
+
+import json
+import os
+from pathlib import Path
+from typing import List
+
+from .render_caddy import SiteMetadata, _expand, _to_bool
+
+
+def load_metadata(config_path: Path) -> List[SiteMetadata]:
+    with config_path.open("r", encoding="utf-8") as fh:
+        data = json.load(fh)
+
+    sites = data.get("sites", [])
+    metadata: List[SiteMetadata] = []
+    for raw_site in sites:
+        site = _expand(raw_site)
+        health_cfg = site.get("health_check") or {}
+        metadata.append(
+            SiteMetadata(
+                name=site.get("name", "site"),
+                health_url=health_cfg.get("url", ""),
+                skip_healthcheck=_to_bool(health_cfg.get("skip"), default=False),
+                app_url=site.get("app_url", ""),
+            )
+        )
+    return metadata