[codex] Speed up long chat sessions

[jamesbrink]

Summary

• speeds up long chat sessions by moving app state behind an external store adapter
• debounces chat draft writes so typing no longer rerenders the full long transcript on every keystroke
• batches response and terminal stream state updates while keeping terminal live events immediate
• windows and memoizes long chat rendering with a load-older control
• makes the terminal panel resizable and persists the selected height

Validation

• bun run typecheck
• bunx vitest run
• bun run lint (0 errors; existing warning in reloadRequired.ts)