feat: scaffold mvp shell and content runtime

js/content/validation/validate-assets.js

@@ -0,0 +1,24 @@
+export function validateAssets(city, assetExists) {
+  const errors = []
+  const warnings = []
+
+  if (typeof assetExists !== 'function') {
+    return { errors, warnings }
+  }
+
+  const assetPaths = [
+    city.cover?.catImage,
+    city.cover?.catThumb,
+    ...(city.elements ?? []).map((element) => element.image),
+  ].filter(Boolean)
+
+  for (const assetPath of assetPaths) {
+    if (!assetExists(assetPath)) {
+      errors.push(`City "${city.id}" asset is missing: ${assetPath}`)
+    }
+  }
+
+  return { errors, warnings }
+}
+
+export default validateAssets