feat(baoyu-url-to-markdown): vendor baoyu-fetch runtime

skills/baoyu-url-to-markdown/scripts/lib/utils/url.ts

@@ -0,0 +1,12 @@
+export function normalizeUrl(input: string): URL {
+  try {
+    return new URL(input);
+  } catch {
+    throw new Error(`Invalid URL: ${input}`);
+  }
+}
+
+export function sanitizeFilename(input: string): string {
+  return input.replace(/[^a-zA-Z0-9._-]+/g, "-").replace(/^-+|-+$/g, "") || "document";
+}
+