[codex] Fix keyboard event detection to use logical keys

[wanxiankai]

Acceptance Checklist:

• Tests
• Documentation and examples (not needed; no public API changes)

Fixes #1030.

What changed

• Detect Tab and Escape with KeyboardEvent.key, which represents the logical key value.
• Keep the existing keyCode fallback for older React/IE environments.
• Update modern keyboard-event tests to exercise key and add a regression test for a physical Escape code that represents a different logical key.

Why

KeyboardEvent.code identifies the physical key location. Some input methods can therefore emit code: "Escape" while key is a non-Escape value such as "Process". The previous check treated that event as Escape and closed the modal unexpectedly while the user was inserting text or emoji.

Validation

• Browser test suite: 86 passed, 0 failed, 0 skipped
• Regression test: should not close when Escape code represents another logical key
• npm run lint
• git diff --check