feat(engine): Android UX sweep — tap-to-move, safe area, HUD polish

Single-tap auto-move (input_plugin):
- Remove 0.5 s double-tap window; any uncommitted TouchPhase::Ended on
  a face-up card now fires MoveRequestEvent immediately.

Bottom safe-area inset (layout, table_plugin):
- compute_layout gains safe_area_bottom param; height budget and bottom
  margin both respect the navigation bar reservation.

Card back contrast (card_plugin):
- CardBackFrame child sprite (gray, card_size + 3 px, local z=-0.01)
  spawned behind every face-down card so the dark back_0.png reads as
  a distinct rectangle against the dark felt.

HUD action bar compactness (hud_plugin):
- max_width 50% → 65% on the action button row; 6 buttons now wrap to
  2 rows instead of 3 on a 360 dp phone.

Dynamic tableau fan fraction (layout, card_plugin):
- Layout gains available_tableau_height field.
- update_tableau_fan_frac system (after GameMutation, before
  sync_cards_on_change) grows face-up fan from 0.25 to the window max
  as revealed column depth increases. Face-down fan is left at the
  window-adaptive value so stacks stay visible.

ModesPopover + MenuPopover light-dismiss (hud_plugin):
- Fullscreen transparent Button backdrop spawned at Z_HUD+4 behind each
  popover; tapping outside the panel despawns both panel and backdrop.

Stock badge legibility (card_plugin):
- Badge font TYPE_CAPTION (11 pt) → TYPE_BODY (14 pt); background
  sprite 28×16 → 34×20 world units.

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

solitaire_engine/src/table_plugin.rs

@@ -163,8 +163,10 @@ fn setup_table(
     // Safe-area insets arrive from JNI asynchronously; they are almost always
     // 0 here (populated ~frame 2-3). on_safe_area_changed fires when they
     // arrive and issues a synthetic WindowResized to re-snap all game objects.
-    let safe_area_top = safe_area.as_deref().copied().unwrap_or_default().top / scale;
-    let layout = compute_layout(window_size, safe_area_top);
+    let insets = safe_area.as_deref().copied().unwrap_or_default();
+    let safe_area_top = insets.top / scale;
+    let safe_area_bottom = insets.bottom / scale;
+    let layout = compute_layout(window_size, safe_area_top, safe_area_bottom);
 
     let selected_bg = settings.as_ref().map_or(0, |s| s.0.selected_background);
 
@@ -300,8 +302,10 @@ fn on_window_resized(
     };
     let window_size = Vec2::new(ev.width, ev.height);
     let scale = windows.iter().next().map_or(1.0, |w| w.scale_factor());
-    let safe_area_top = safe_area.as_deref().copied().unwrap_or_default().top / scale;
-    let new_layout = compute_layout(window_size, safe_area_top);
+    let insets = safe_area.as_deref().copied().unwrap_or_default();
+    let safe_area_top = insets.top / scale;
+    let safe_area_bottom = insets.bottom / scale;
+    let new_layout = compute_layout(window_size, safe_area_top, safe_area_bottom);
 
     if let Some(layout_res) = layout_res.as_deref_mut() {
         layout_res.0 = new_layout.clone();