feat(engine): Phase F touch action bar — thumb-reach Undo/Draw/Hint + hold-to-repeat undo

Touch layout (USE_TOUCH_UI_LAYOUT) restructures the bottom action bar
to five buttons: an enlarged Undo / Draw / Hint trio (96x64px targets,
1.35x labels) between compact Menu and Pause. Draw is new — it fires
the same DrawRequestEvent as tapping the stock, so the most frequent
action no longer needs a reach to the top of a tall folded screen.
Help, Modes, and New Game leave the touch bar (they live in Menu ->
System, the Home grid, and Home's hero respectively). Desktop keeps
the seven-button bar unchanged (decision 5: touch-only).

Holding Undo now steps back repeatedly after a 0.45s delay (5.5/s),
each step through the normal request path so the scoring penalty
applies. New self-ambiguous DrawRequestWriters set keeps the ambiguity
gate at zero with the fourth DrawRequestEvent writer.

6 new hud_plugin tests; workspace suite + clippy green.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

solitaire_engine/src/hud_plugin/updates.rs

@@ -554,11 +554,11 @@ pub(super) fn action_bar_font_size(window_width: f32) -> f32 {
 
 pub(super) fn action_button_metrics() -> (UiRect, Val, Val) {
     if USE_TOUCH_UI_LAYOUT {
-        // Tight 3 px horizontal padding (down from 4) trims 14 px off the row
-        // total across 7 buttons, and a 44 px min_width (down from 52) lets the
-        // shortest labels ("New", "Help") shrink to their text rather than
-        // padding the row out past the 900 logical-px viewport. min_height
-        // stays at 44 px to preserve the comfortable touch target.
+        // Tight 3 px horizontal padding keeps the compact buttons narrow;
+        // Phase F trimmed the touch bar to 5 buttons (2 compact + 3
+        // primary), so width pressure is lower than the old 7-button row.
+        // min_height stays at 44 px to preserve the comfortable touch
+        // target on the compact buttons.
         (
             UiRect::axes(Val::Px(3.0), Val::Px(4.0)),
             Val::Px(44.0),
@@ -573,6 +573,20 @@ pub(super) fn action_button_metrics() -> (UiRect, Val, Val) {
     }
 }
 
+/// Metrics for the touch bar's enlarged Undo / Draw / Hint trio (Phase F).
+/// 96×64 px targets — comfortably past the 44 px accessibility floor and
+/// big enough to hit one-handed without looking. Only the touch layout
+/// spawns primary buttons, so no desktop branch is needed; the desktop
+/// values exist purely so host-side tests can exercise the touch spawn
+/// path with sensible numbers.
+pub(super) fn primary_action_button_metrics() -> (UiRect, Val, Val) {
+    (
+        UiRect::axes(Val::Px(10.0), Val::Px(8.0)),
+        Val::Px(96.0),
+        Val::Px(64.0),
+    )
+}
+
 pub(super) fn spawn_action_button_label(
     parent: &mut ChildSpawnerCommands,
     label: &str,