fixup! diigo-cache: RSS in diigo's export shape, from cached items

compare-export.ts: exit 2 on bad usage is an external convention, so its
@file cites the source (Bash Reference Manual §3.7.5, Exit Status).

Generated-by: Claude Opus 5.5

diigo-cache/scripts/compare-export.ts

@@ -8,7 +8,9 @@
  * the export, keyed on link: title, tags, description, highlights and
  * sticky notes. Prints counts to stdout; writes <out-dir>/from-cache.rss
  * and <out-dir>/report.json (mismatched links, by category). Exits 2 on
- * bad usage.
+ * bad usage, the shell's convention.
+ *
+ * @see https://www.gnu.org/software/bash/manual/html_node/Exit-Status.html
  */
 import * as nodeFs from "node:fs/promises";
 import { basename, join } from "node:path";