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/input_plugin/mod.rs

@@ -136,11 +136,22 @@ impl Plugin for InputPlugin {
             .add_systems(
                 Update,
                 (
-                    handle_keyboard_core,
+                    // The three `DrawRequestEvent` writers join the
+                    // self-ambiguous `DrawRequestWriters` set so the HUD's
+                    // touch Draw button (hud_plugin, Phase F) can write the
+                    // same queue without tripping the ambiguity gate. The
+                    // `.chain()` still orders them relative to each other.
+                    handle_keyboard_core
+                        .in_set(crate::game_plugin::DrawRequestWriters)
+                        .ambiguous_with(crate::game_plugin::DrawRequestWriters),
                     handle_keyboard_hint,
                     handle_keyboard_forfeit,
-                    handle_stock_click,
-                    handle_touch_stock_tap,
+                    handle_stock_click
+                        .in_set(crate::game_plugin::DrawRequestWriters)
+                        .ambiguous_with(crate::game_plugin::DrawRequestWriters),
+                    handle_touch_stock_tap
+                        .in_set(crate::game_plugin::DrawRequestWriters)
+                        .ambiguous_with(crate::game_plugin::DrawRequestWriters),
                     handle_double_click,
                     // Mouse drag pipeline.
                     start_drag,