Adds a top-level `log_dir` config key (defaults to `$CODEX_HOME/log`) so
one-off runs can redirect `codex-tui.log` via `-c`, e.g.:
codex -c log_dir=./.codex-log
Also resolves relative paths in CLI `-c/--config` overrides for
`AbsolutePathBuf` values against the effective cwd (when available).
Tests:
- cargo test -p codex-core
## Summary
- preserve baseline streaming behavior (smooth mode still commits one
line per 50ms tick)
- extract adaptive chunking policy and commit-tick orchestration from
ChatWidget into `streaming/chunking.rs` and `streaming/commit_tick.rs`
- add hysteresis-based catch-up behavior with bounded batch draining to
reduce queue lag without bursty single-frame jumps
- document policy behavior, tuning guidance, and debug flow in rustdoc +
docs
## Testing
- just fmt
- cargo test -p codex-tui
