feat(skills): add reply-router skill

[codeboost-tr]

Add reply-router skill: classifies inbound email replies, suppresses unsubscribes via data-store CAS append_event, emits typed routing decisions for non-unsubscribe replies, and escalates ambiguous or unsealed inputs to human review.

Package structure

• skills/reply-router/X.yaml - graph runner with 2 harness cases
• skills/reply-router/SKILL.md - metadata and documentation
• skills/reply-router/run.mjs - runner entry point
• skills/reply-router/classify.mjs - reply classification logic
• skills/reply-router/append_event.mjs - suppression event writer
• skills/reply-router/emit_route.mjs - routing decision emitter
• skills/reply-router/fixtures/ - test fixtures for both harness cases
• skills/reply-router/evidence/ - verification evidence and report

Harness cases

1. sealed_unsubscribe_suppression - sealed unsubscribe reply ? suppression append_event, no routing
2. stop_ambiguous_or_unsealed - ambiguous or unsealed receipt ? needs_agent, no state mutation