Test runner

The checks the library is held to, run on the live source. To edit a test: click Accept output when what the library produced is right, or click an expected value to change it in place (Enter saves, Esc cancels). Edit row opens every column; Add a test starts a row and can fill it from the current output.

Same checks as npm test (test/checks.js), run on the live source in src/ — reload after editing code. Accept writes the generated output into the test file as the new expected value. Fail: output doesn't match. Known: doesn't match, listed in test/known-failures.json. Fixed: listed there but now passes — remove it from the list. Editing needs the dev server (npm run serve); with any other server the page is read-only. The old test editor is still here.