Implement a status endpoint that returns the current state of the
scraper system. The response includes mutex state (idle/running with
job ID), last run history from scraper_runs collection (status,
timing, unit/error counts), next scheduled run timestamp, and
cron schedule expression.
Protected by requireAuth + requireAdmin middleware. Returns 503
on database errors for graceful degradation. Includes 13 tests
covering auth, response structure, edge cases, and error handling.
