Fix TUI issues with Alt-Gr on Windows

[etraut-openai]

This PR fixes keyboard handling for the Right Alt (aka "Alt-Gr") key on Windows. This key appears on keyboards in Central and Eastern Europe. Codex has effectively never worked for Windows users in these regions because the code didn't properly handle this key, which is used for typing common symbols like \ and @.

A few days ago, I merged a community-authored PR that supplied a partial fix for this issue. Upon closer inspect, that PR was 1) too broad (not scoped to Windows only) and 2) incomplete (didn't fix all relevant code paths, so paste was still broken).

This improvement is based on another community-provided PR by @marektomas-cz. He submitted it back in September and later closed it because it didn't receive any attention.

This fix addresses the following bugs: #5922, #3046, #3092, #3519, #5684, #5843.

[etraut-openai]

@codex review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. Swish!

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[nornagon-openai]

logic looks correct but i'd prefer this get integrated into key_hint.rs instead of one-off'd in various places to ensure consistent behavior.

[etraut-openai]

OK, I moved the is_altgr function to key_hint.rs and added a new has_ctrl_or_alt helper function. Is that what you had in mind?

[nornagon-openai]

ah sure, i think i actually slightly misunderstood this and thought there was a specific AltGr code you were trying to catch (or avoid catching), but this is on arbitrary chars. lgtm.

[joshka-oai]

There's some long standing work on AltGr in crossterm that has a bit more context on this problem. The main part of solving it in the followup PRs was that doing something that works on keyboards that do have AltGr keys, broke things on keyboards without it. I haven't looked at the solution here (only the description), but it's worth noting that it may have a similar problem where fixing the problem for international keyboards introduces a problem for non international keyboards. It may be that we don't have this problem at the app layer however.

crossterm-rs/crossterm#820
crossterm-rs/crossterm#917
crossterm-rs/crossterm#937

(not a blocker - merely awareness / context)