fix(mobile): keep keyboard accessory row height stable (#31363)

fix(mobile): keep keyboard accessory row height stable
Stretch the dismiss control within the accessory row so showing it no
longer adds height and needlessly reduces the terminal viewport.

Adapted from community PR #23511 by @innocarpe.

Co-authored-by: Wooseong Kim <innocarpe@gmail.com>
Co-authored-by: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

mobile/src/session/mobile-session-command-input-styles.ts

@@ -121,14 +121,14 @@ export const mobileSessionCommandInputStyles = StyleSheet.create({
   keyboardDismissKey: {
     alignItems: 'center',
     justifyContent: 'center',
+    alignSelf: 'stretch',
     marginLeft: spacing.sm,
     marginVertical: spacing.xs,
     backgroundColor: colors.bgRaised,
     paddingHorizontal: spacing.sm + 2,
     paddingVertical: 0,
     borderRadius: radii.button,
-    minWidth: 36,
-    height: 28
+    minWidth: 36
   },
   keyboardDismissGlyph: {
     alignItems: 'center',