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>

docs/android/PLAYABILITY_TODO.md

@@ -66,9 +66,16 @@ rewrites required.
 
 ## P1 — Touch UX
 
-- [ ] **Suppress keyboard-hint labels on Android.** Gate the `Esc / A /
-  N / []` accelerator chips behind `#[cfg(not(target_os = "android"))]`
-  in the HUD spawn site(s).
+- [x] **Suppress keyboard-hint labels on Android.** *Closed
+  2026-05-10.* `spawn_action_button` now nulls the `hotkey`
+  argument on Android via a `#[cfg(target_os = "android")]` rebind,
+  so the U / Esc / F1 / N chips next to the action row labels
+  disappear on touch builds. Other hint sites (onboarding panel,
+  pause-modal `Esc` hint, mode-card hotkey chips on the home
+  screen, replay overlay footer, modal toggle hints in
+  profile/stats/leaderboard/settings, help screen) survive — they
+  live behind navigation and a touch user reaches them less often.
+  Track as a P3 sweep when more screens are audited on hardware.
 - [ ] **Thumb-sized hit targets.** HUD buttons sized for mouse;
   Material guideline minimum is 44–48 dp. Increase button paddings
   on touch builds.