fix(codex): align SDK with supported models

[devswha]

Summary

• pin @openai/codex-sdk and its bundled CLI to 0.144.6
• keep ChatMux history/resume turns compatible with models recorded by current Codex CLI sessions
• add a regression guard that prevents SDK and bundled CLI versions from drifting

Reproduction

1. Create a Codex 0.144.6 tmux session using gpt-5.6-sol.
2. Let ChatMux synchronize the transcript, terminate the tmux session, and reopen it from history.
3. Send a follow-up prompt.
4. The previous 0.141.0 SDK fails with: The 'gpt-5.6-sol' model requires a newer version of Codex.

Verification

• Codex provider tests: 5/5
• npm run typecheck
• npm run lint
• npm run build
• actual browser E2E follow-up on the synchronized Codex transcript

[devswha]

E2E QA evidence (2026-07-22): the old 0.141.0 SDK failed twice with the newer-model error. With SDK and bundled CLI 0.144.6, the same browser history-resume flow completed with CHATMUX_E2E_CODEX_T2 value=CODEX_T1. Final npm run verify passed.