watchDrill(fetch, sleep) polls a forge until it is healthy again and returns each distinct line it said while unhealthy #2424

Replaces #2393. Its reds ('the pages', 'token counts on the pages') were in suites it did not touch, so it waits for the runner fix.

Done looks like:

• [ ] A pure scripts/drills/watch.ts exports watchDrill({url, fetch, sleep, limit}), which returns {startedAt, healthyAt, lines} or a timeout. No stdin, no posting, no globals.
• [ ] A test with an injected fetch and sleep runs without real waiting.