Fix handle_shortcut_overlay_key for cross-platform consistency (#7583)

**Summary**
- Shortcut toggle using `?` in `handle_shortcut_overlay_key` fails to
trigger on some platforms (notably Windows). Current match requires
`KeyCode::Char('?')` with `KeyModifiers::NONE`. Some terminals set
`SHIFT` when producing `?` (since it is typically `Shift + /`), so the
strict `NONE` check prevents toggling.

**Impact**
- On Windows consoles/terminals, pressing `?` with an empty composer
often does nothing, leading to inconsistent UX compared to macOS/Linux.

**Root Cause**
- Crossterm/terminal backends report modifiers inconsistently across
platforms. Generating `?` may include `SHIFT`. The code enforces
`modifiers == NONE`, so valid `?` presses with `SHIFT` are ignored.
AltGr keyboards may also surface as `ALT`.

**Repro Steps**
- Open the TUI, ensure the composer is empty.
- Press `?`.
- Expected: Shortcut overlay toggles.
- Actual (Windows frequently): No toggle occurs.

**Fix Options**
- Option 1 (preferred): Accept `?` regardless of `SHIFT`, but reject
`CONTROL` and `ALT`.
- Rationale: Keeps behavior consistent across platforms with minimal
code change.
	- Example change:
		- Before: matching `KeyModifiers::NONE` only.
		- After: allow `SHIFT`, disallow `CONTROL | ALT`.
		- Suggested condition:
			```rust
			let toggles = matches!(key_event.code, KeyCode::Char('?'))
&& !key_event.modifiers.intersects(KeyModifiers::CONTROL |
KeyModifiers::ALT)
					&& self.is_empty();
			```

- Option 2: Platform-specific handling (Windows vs non-Windows).
- Implement two variants or conditional branches using `#[cfg(target_os
= "windows")]`.
- On Windows, accept `?` with `SHIFT`; on other platforms, retain
current behavior.
- Trade-off: Higher maintenance burden and code divergence for limited
benefit.

---

close #5495

codex-rs/tui/src/bottom_pane/chat_composer.rs

@@ -1504,14 +1504,9 @@ impl ChatComposer {
             return false;
         }
 
-        let toggles = matches!(
-            key_event,
-            KeyEvent {
-                code: KeyCode::Char('?'),
-                modifiers: KeyModifiers::NONE,
-                ..
-            } if self.is_empty()
-        );
+        let toggles = matches!(key_event.code, KeyCode::Char('?'))
+            && !has_ctrl_or_alt(key_event.modifiers)
+            && self.is_empty();
 
         if !toggles {
             return false;