feat(signal,ruvector): ADR-138 LinkGroup/ArrayCoordinator clock-quality gating (#842)

- ruvector viewpoint/coherence.rs: ClockQualityScore, ClockQualityGate,
  ClockGateDecision (Admit/MonitorOnly/Reject), ClockRejectReason. 200us floor,
  9s staleness ceiling per ADR-110.
- signal ruvsense/array_coordinator.rs: ArrayCoordinator domain service +
  DirectionalEvidence. Gates nodes, computes GDI + Cramer-Rao credence, builds
  attention weights (real node_attention_weights when amplitudes present, else
  clock-quality softmax), emits CoherenceDrop + GeometryInsufficient flags.
- Cycle resolution: ArrayCoordinator lives in signal (depends on ruvector), not
  ruvector, so it can emit ADR-137 canonical ContradictionFlag. Documented.
- 8 tests (5 coordinator + 3 clock gate); workspace 0 errors.

Co-Authored-By: claude-flow <ruv@ruv.net>