## Why
Issue #23031 was hard to diagnose from existing `codex doctor` output
because support could not see the OS language, resolved Git install, Git
repo metadata, Windows console mode/code page, or terminal-title inputs
that affect the TUI startup path. This adds those read-only signals to
`codex doctor` so Windows, Linux, and macOS reports carry the context
needed to investigate similar terminal rendering regressions.
Refs #23031
## What Changed
- Add a `system.environment` check for OS type/version, OS language, and
locale env vars.
- Add a `git.environment` check for the selected Git executable, PATH
Git candidates, version, exec path/build options, repository root,
branch, `.git` entry, and `core.fsmonitor`.
- Add Windows console code page and VT-processing mode details to
terminal diagnostics.
- Add a `terminal.title` check for configured/default title items and
resolved project-title source/value.
- Surface startup warning counts in config diagnostics and teach human
output to render the new categories.
## How to Test
1. On Windows, check out this branch and run `cargo run -p codex-cli --
doctor --summary`.
2. Confirm the Environment section includes `system`, `git`, `terminal`,
and `title` rows.
3. Run `cargo run -p codex-cli -- doctor --json`.
4. Confirm the JSON contains `system.environment`, `git.environment`,
and `terminal.title`; on Windows, confirm `terminal.env` details include
console code pages and `VT processing` for stdout/stderr.
5. From a non-git directory, run the same `doctor --json` command and
confirm the Git check reports `repo detected: false` rather than
warning.
Targeted tests:
- `cargo test -p codex-cli doctor`
- `cargo test -p codex-cli`
