[codex] improve list json and proxy maintenance

[Dikevin]

Summary

• Add saved account paths to codexm list --json and codexm list <name> --json, with README/spec/skill docs updated.
• Tighten auth repair advice so quota refresh timeouts do not suggest codexm replace; only broken auth refresh plus expired/near-expiry tokens do.
• Split high-churn helpers out of watch history, proxy HTTP handling, and shared time formatting; split proxy list/aggregate tests into a focused file.

Validation

• pnpm docs:readme
• pnpm typecheck
• pnpm test
• pnpm build
• git diff --check origin/master..HEAD
• Isolated built-artifact live read validation with temp HOME/CODEX_HOME: current --json, list --json, and list <name> --json verified saved account paths.

Notes

• No live daemon/proxy/Desktop process was stopped, restarted, or repointed during validation.