07806e55

By: ValentinHirschi <valentin.hirschi@gmail.com>

Tighten the five-hour limits wording and the A381 sign-split regression

- docs/USAGE.md: the five-hour ceiling applies to campaign_time_secs of every
  symgcad bench configuration and to solve/verify timeouts of completion and
  ablation campaigns; a plain benchmark's solve_timeout_secs is only required
  to be positive and is cut to the remaining campaign budget.
- tests/a381_mz2_half.rs: assert the documented 158 F<0 / 678 F>0 split
  instead of only the presence of both signs.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>