feat: support multiple paired anchors

[Microck]

Summary

• store multiple paired anchors on iPhone instead of a single replacement slot
• bind each session to the exact anchor that started it, and require that same anchor for release
• add per-anchor rename/remove UI, active-anchor messaging, and multi-anchor view-model coverage

Testing

• docker run --rm -v "$PWD/ios:/workspace" -w /workspace swift:5.10-jammy swift test
• GitHub Actions ios-sideload-lite-ipa: run 23932804808
• BrowserStack real-device flow against signed build 8
• Evidence:
  • /tmp/browserstack-multi-anchor/10-after-arm.xml: 2 anchors are paired. Desk anchor must release the current session. and desk...2222
  • /tmp/browserstack-multi-anchor/11-after-wrong-release.xml: That anchor does not match the release anchor for this session. and Wrong anchor
  • /tmp/browserstack-multi-anchor/12-after-release.xml: Released via Desk anchor and Tap to Start New Session