refactor: remove some duplicated code

lib/string.ts

@@ -2,3 +2,16 @@ export function formatDate(date: Date): string {
   const options = { year: "numeric", month: "long", day: "numeric" } as const;
   return new Intl.DateTimeFormat("en-US", options).format(date);
 }
+
+export function safeFileName(inputString: string): string {
+  // Convert the string to lowercase
+  let fileName = inputString.toLowerCase();
+
+  // Replace spaces with underscores
+  fileName = fileName.replace(/ /g, "_");
+
+  // Remove characters that are not safe for file names
+  fileName = fileName.replace(/[^\w.-]/g, "");
+
+  return fileName;
+}