fix(tui) Support image paste from clipboard on native Windows (#7514)

Closes #3404 

## Summary
On windows, ctrl+v does not work for the same reason that cmd+v does not
work on macos. This PR adds alt/option+v detection, which allows windows
users to paste images from the clipboard using.

We could swap between just ctrl on mac and just alt on windows, but this
felt simpler - I don't feel strongly about it.

Note that this will NOT address image pasting in WSL environments, due
to issues with WSL <> Windows clipboards. I'm planning to address that
in a separate PR since it will likely warrant some discussion.

## Testing
- [x] Tested locally on a Mac and Windows laptop

codex-rs/tui/src/chatwidget.rs

@@ -1383,7 +1383,9 @@ impl ChatWidget {
                 modifiers,
                 kind: KeyEventKind::Press,
                 ..
-            } if modifiers.contains(KeyModifiers::CONTROL) && c.eq_ignore_ascii_case(&'v') => {
+            } if modifiers.intersects(KeyModifiers::CONTROL | KeyModifiers::ALT)
+                && c.eq_ignore_ascii_case(&'v') =>
+            {
                 match paste_image_to_temp_png() {
                     Ok((path, info)) => {
                         self.attach_image(