add legacy image rewrite helper

src/lib/legacy-image.ts exports rewriteLegacyImageUrl(url) and
rewriteLegacyImageUrlsInHtml(html) which translate WP origin URLs
(https://www.broadcastbeat.com/wp-content/uploads/...) to local paths
under /legacy/... served from the new persistent storage volume mounted
at /app/public/legacy/.

src/lib/legacy-image-map.json holds 3,856 URL→path entries built in
Phase 2: 3,839 featured images (mostly converted to webp, q=85) plus
27 ad creatives plus the site logo.

Use this helper at server-render time when emitting <img>/<Image> for
imported WP articles, so the 707 MB on-host cache replaces external
fetches to the origin.

src/lib/legacy-image.ts

@@ -0,0 +1,34 @@
+import map from "./legacy-image-map.json";
+
+const LEGACY_MAP = map as Record<string, string>;
+
+const LEGACY_HOSTS = [
+  "https://www.broadcastbeat.com",
+  "https://broadcastbeat.com",
+  "http://www.broadcastbeat.com",
+  "http://broadcastbeat.com",
+];
+
+export function rewriteLegacyImageUrl(url: string | null | undefined): string {
+  if (!url) return "";
+  // Direct map hit (canonical https://www.broadcastbeat.com/...)
+  const direct = LEGACY_MAP[url];
+  if (direct) return direct;
+  // Try alternate-host normalization
+  for (const host of LEGACY_HOSTS) {
+    if (url.startsWith(host)) {
+      const path = url.slice(host.length);
+      const canonical = `https://www.broadcastbeat.com${path}`;
+      const hit = LEGACY_MAP[canonical];
+      if (hit) return hit;
+    }
+  }
+  return url;
+}
+
+export function rewriteLegacyImageUrlsInHtml(html: string): string {
+  return html.replace(
+    /(https?:\/\/(?:www\.)?broadcastbeat\.com\/wp-content\/uploads\/[^"'\s)]+)/g,
+    (m) => rewriteLegacyImageUrl(m),
+  );
+}