release v3.1.2

- Pieces (Torre/Alfil/Caballo/Reina/Peón) as real subagents + blackboard MCP (BREAKING)
- Service v2.11: Command Center dashboard + /blackboard/api/*
- Smoke-6 audit-trail endpoint suite
- Council (four-voice deliberation skill)
- Gateguard (pre-edit fact-forcing hook)
- Rey model escalator
- chore: enable 4 soviet MCP servers in local settings

Reina gate: PASS · 3 P2 follow-ups (dashboard.html LOC, create_session refactor, missing Task-ID on 9bb0e75)