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

compare-export.ts: the usage message comes from the @file manual's
synopsis line (read from the script's own source, on the bad-usage path
only), docopt-style, so the synopsis lives in one place; if the header
changes shape, it says "see the @file comment".

Generated-by: Claude Opus 5.5

diigo-cache/scripts/compare-export.ts

@@ -146,7 +146,10 @@ export async function main(
 ): Promise<void> {
 	const [dbPath, exportPath, outPath] = argv;
 	if (!dbPath || !exportPath || !outPath) {
-		stderr.write("usage: node scripts/compare-export.ts <cache.sqlite> <export.xml> <out-dir>\n");
+		// the @file comment is the manual: its indented synopsis line is the usage
+		const source = await fs.readFile(import.meta.filename, "utf8");
+		const synopsis = source.match(/^ \* +(node \S+\.ts .*)$/m)?.[1] ?? "see the @file comment";
+		stderr.write(`usage: ${synopsis}\n`);
 		return exit(BAD_USAGE);
 	}
 	const cache = cacheItems(connect(dbPath));