Replace the implicit "strength = 1" clash rule with a configurable per-vessel,
per-rank requirement (director decision). Adds VesselRankRequirement
{vesselId, rankId, minStrength} (migration crewing_vessel_rank_requirement) and
reworks lib/leave-clash.ts → leaveCausesClash: a leave approval clashes when the
remaining active same-rank cover over the window would fall below minStrength
(default 1 when unconfigured), auto-raising a LEAVE requisition. The requirement
is managed by the office (manage_crew, admin UI in the follow-up).
- Integration: leave-attendance.test.ts gains a configured-strength case
(minStrength 2, one remaining → clash). Full unit (240) + integration (183) green.
- CLAUDE.md updated.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>