release: 2.7.0 — delivery correctness and Windows

- CHANGELOG [2.7.0]: the failed-row retry loop (#113), the silent inbox (#114),
  Windows install and wake (#112, #115), the per-session wake cursor (#111)
- README: version badge and What's New in v2.7, crediting @lichtpfad for the
  cross-host findings
- versions: root 2.7.0, core 0.6.0, broker-nats 0.3.2, broker-ws 0.2.1,
  mcp-server 0.2.1; every intra-workspace range moved in the same commit so
  npm ci stays in sync

npm test green: 242/242.