fix(remote): forward Codex usage snapshots over SSH

[F21HGG]

Summary

• emit a codex_usage message from the remote bridge using the newest Codex rollout quota and token snapshot
• merge local and remote quota snapshots by capture time while keeping remote token baselines qualified by SSH host
• resend the current snapshot when an SSH control client attaches and cache unchanged rollout scans
• document the forwarded usage data and add protocol, selection, analytics, and bridge coverage

Why

Remote Codex hook notifications and app-server thread events already reached Ping Island over SSH, but usage loading only scanned the Mac's local ~/.codex/sessions. As a result, sessions running exclusively on a remote host did not contribute usage data.

Validation

• git diff --check
• swiftc -frontend -parse for all changed Swift sources and tests
• swift build --package-path Prototype --product PingIslandBridge
• direct Unix-socket bridge check confirmed a live codex_usage payload with plan, quota windows, and token totals

Environment limitations

• swift test --package-path Prototype --filter remoteAgentForwardsCodexUsageSnapshots is currently blocked in this Command Line Tools environment by the existing test target error no such module Testing
• macOS app tests were not run because full Xcode is not installed on the validation machine

[erha19]

@F21HGG 感谢提交，CI 检查未通过，麻烦解决一下

[F21HGG]

@erha19 维护者您好，#296 已修复此前的 CI 问题，我也已将本 PR 更新到最新 main。新的 CI 正在等待批准，麻烦您有空时帮忙点击 Approve and run，谢谢！