fix: npm test script fails with bare directory arg

\`node --test tests/\` throws MODULE_NOT_FOUND on this Node CLI (it
resolves the bare directory as a CommonJS entry module instead of a
test-runner glob) — this was masked locally all session because every
manual verification used \`node --test tests/*.test.mjs\` directly,
never the actual \`npm test\` script. CI caught it on the first real
run. Fixed package.json's test script to use the explicit glob.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

package.json

@@ -26,7 +26,7 @@
   ],
   "scripts": {
     "validate": "node scripts/validate.mjs",
-    "test": "node --test tests/",
+    "test": "node --test tests/*.test.mjs",
     "lh": "node src/cli.mjs",
     "onboard": "node scripts/onboard.mjs"
   },