test(scripts): wire scripts/**/*.test.mjs under a vitest runner

241 tests across 16 script test files were wired to NO runner (the
generators vitest config never included them and several used node:test
imports that vitest silently skips). New root vitest.scripts.config.mjs
+ pnpm test:scripts + a CI validate step run them all; node:test imports
converted to vitest keeping node:assert. Split out of 8c88a9a where a
concurrent agent's staged files were swept into the marketing-pages
commit.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

scripts/coverage/aggregate.test.mjs

@@ -1,4 +1,6 @@
-import { test, describe } from "node:test";
+// Runs under vitest (pnpm test:scripts picks up scripts/**/*.test.mjs);
+// node:assert keeps the original assertion style.
+import { test, describe } from "vitest";
 import assert from "node:assert/strict";
 import fs from "node:fs";
 import path from "node:path";