fix(tui): Windows Alt/AltGr punctuation and “?” overlay

[esdrasrenan]

Problem

On Windows with international keyboards (AltGr), / and ? could be blocked.
? did not always open the overlay when the terminal did not report Shift.

Solution

TextArea

• Insert characters with NONE/SHIFT.
• Allow Alt/AltGr for punctuation (e.g., /, ?).
• Preserve Alt+f, Alt+b, and Ctrl+Alt+h.

Overlay

• On empty line, ? toggles shortcuts (including AltGr).
• With text, ? just inserts.

Validation

Windows (VS Code / Windows Terminal):

• Empty line → Alt+W opens/closes overlay.
• With text → ? inserts.
• / inserts (incl. AltGr).
• Alt+Backspace and Ctrl+Alt+H delete word.

Scope

Only codex-rs/tui.

Tests

cargo test -p codex-tui → 387/387 passed.

References

Fixes #4260

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[esdrasrenan]

I have read the CLA Document and I hereby sign the CLA