fix(android): hide keyboard-hint chips on action buttons

The U / Esc / F1 / N caption chips next to the HUD action buttons
are meaningless on a touch device and visibly clutter the
narrow-viewport action row (visible as "Esc A [] N" in the v0.22.3
screenshot). `spawn_action_button` now rebinds `hotkey` to `None`
under `#[cfg(target_os = "android")]` so the chip-spawn branch is
skipped on touch builds.

Menu / Modes chevrons are unaffected — they indicate dropdown
behaviour and still apply on touch. Other hint surfaces
(onboarding, pause modal Esc hint, mode-card chips, replay
footer, modal toggle chips, help screen) live behind navigation
and are tracked as a P3 sweep in PLAYABILITY_TODO.md.

Closes P1 #1 of docs/android/PLAYABILITY_TODO.md. 855 engine
tests pass; clippy clean.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

solitaire_engine/src/hud_plugin.rs

@@ -730,6 +730,14 @@ fn spawn_action_button<M: Component>(
     font: &TextFont,
     order: i32,
 ) {
+    // Hotkey hint chips ("U", "Esc", "F1", "N") are meaningless on a
+    // touch device — the button itself is the affordance — and they
+    // visibly clutter the narrow-viewport action row. Force the hint
+    // off on Android; the chevrons on Menu/Modes remain because they
+    // indicate dropdown behaviour and still apply on touch.
+    #[cfg(target_os = "android")]
+    let hotkey: Option<&'static str> = None;
+
     let hotkey_font = TextFont {
         font: font.font.clone(),
         font_size: TYPE_CAPTION,