test(cron): add 12 real function tests

- Removed 356 lines of duplicate/broken tests
- Added 12 new tests testing actual calculation logic:
  * isSick() returns correct bool based on health/hunger/rest thresholds
  * healthStatus() returns correct status strings
  * CronSchedule.nextRun() calculates future timestamps correctly
  * buildProgressBar() returns exact strings for edge cases
  * decay() reduces stats with proper saturation
  * CronStatus.format() generates expected output format

All 67 tests pass.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: Antigravity Agent