feat(engine,data): add tap-to-select touch input mode (#70)

- Add TouchInputMode enum (OneTap | TapToSelect) to solitaire_data settings
- Create TouchSelectionPlugin with TouchSelectionState resource and highlight
- Branch handle_double_tap: OneTap → existing auto-move, TapToSelect → two-tap flow
- Add Settings UI toggle row (Touch Input Mode) with TouchInputModeText marker
- Register TouchSelectionPlugin in CoreGamePlugin

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

solitaire_engine/src/settings_plugin.rs

@@ -141,6 +141,10 @@ struct HighContrastText;
 #[derive(Component, Debug)]
 struct ReduceMotionText;
 
+/// Marks the `Text` node showing the current touch input mode state.
+#[derive(Component, Debug)]
+struct TouchInputModeText;
+
 /// Marks the `Text` node showing the live tooltip-delay value.
 #[derive(Component, Debug)]
 struct TooltipDelayText;
@@ -230,6 +234,10 @@ enum SettingsButton {
     /// non-essential motion (card-slide animations become instant
     /// snaps) per `design-system.md` §Accessibility (#3).
     ToggleReduceMotion,
+    /// Toggle [`Settings::touch_input_mode`] between `OneTap`
+    /// (auto-move on tap, default) and `TapToSelect` (first tap selects
+    /// a card/stack, second tap on a target pile moves it).
+    ToggleTouchInputMode,
     /// Toggle the [`Settings::winnable_deals_only`] flag. When on, new
     /// random Classic-mode deals are filtered through
     /// [`solitaire_core::solver::try_solve`] until one is provably
@@ -303,6 +311,7 @@ impl SettingsButton {
             // run before continuing to the picker rows.
             SettingsButton::ToggleHighContrast => 61,
             SettingsButton::ToggleReduceMotion => 62,
+            SettingsButton::ToggleTouchInputMode => 63,
             // Picker rows — every swatch in a row shares the row's
             // priority so entity-index tiebreaking yields left → right.
             SettingsButton::SelectCardBack(_) => 70,
@@ -405,11 +414,17 @@ impl Plugin for SettingsPlugin {
                     update_high_contrast_borders.run_if(resource_changed::<SettingsResource>),
                     update_high_contrast_backgrounds.run_if(resource_changed::<SettingsResource>),
                     update_reduce_motion_text,
+                    update_touch_input_mode_text,
                     update_tooltip_delay_text,
                     update_time_bonus_multiplier_text,
                     update_replay_move_interval_text,
                     update_winnable_deals_only_text,
                     update_smart_default_size_text,
+                ),
+            );
+            app.add_systems(
+                Update,
+                (
                     update_analytics_enabled_text,
                     attach_focusable_to_settings_buttons,
                 ),
@@ -769,6 +784,18 @@ fn update_reduce_motion_text(
     }
 }
 
+fn update_touch_input_mode_text(
+    settings: Res<SettingsResource>,
+    mut text_nodes: Query<&mut Text, With<TouchInputModeText>>,
+) {
+    if !settings.is_changed() {
+        return;
+    }
+    for mut text in &mut text_nodes {
+        **text = touch_input_mode_label(&settings.0.touch_input_mode);
+    }
+}
+
 /// Refreshes the live "Winnable deals only" toggle value in the
 /// Gameplay section whenever `SettingsResource` changes (button click,
 /// hand-edited `settings.json` reload, etc.).
@@ -1177,6 +1204,16 @@ fn handle_settings_buttons(
                     **t = on_off_label(settings.0.reduce_motion_mode);
                 }
             }
+            SettingsButton::ToggleTouchInputMode => {
+                use solitaire_data::settings::TouchInputMode;
+                settings.0.touch_input_mode = match settings.0.touch_input_mode {
+                    TouchInputMode::OneTap => TouchInputMode::TapToSelect,
+                    TouchInputMode::TapToSelect => TouchInputMode::OneTap,
+                };
+                persist(&path, &settings.0);
+                changed.write(SettingsChangedEvent(settings.0.clone()));
+                // Text refreshed by `update_touch_input_mode_text` next frame.
+            }
             SettingsButton::ToggleWinnableDealsOnly => {
                 settings.0.winnable_deals_only = !settings.0.winnable_deals_only;
                 persist(&path, &settings.0);
@@ -1311,6 +1348,14 @@ fn winnable_deals_only_label(enabled: bool) -> String {
     if enabled { "ON".into() } else { "OFF".into() }
 }
 
+fn touch_input_mode_label(mode: &solitaire_data::settings::TouchInputMode) -> String {
+    use solitaire_data::settings::TouchInputMode;
+    match mode {
+        TouchInputMode::OneTap => "One-tap".into(),
+        TouchInputMode::TapToSelect => "Tap to select".into(),
+    }
+}
+
 /// Display string for the "Smart window size" toggle. The argument
 /// is the *enabled* state (i.e. the inverse of the underlying
 /// `disable_smart_default_size` field) so reading the label gives
@@ -1761,6 +1806,15 @@ fn spawn_settings_panel(
                 "Skips card-slide animations and other non-essential motion. Cards snap instantly to their target.",
                 font_res,
             );
+            toggle_row(
+                body,
+                "Touch Input Mode",
+                TouchInputModeText,
+                touch_input_mode_label(&settings.touch_input_mode),
+                SettingsButton::ToggleTouchInputMode,
+                "One-tap: tap a card to auto-move it. Tap to select: first tap selects a card, second tap on a pile moves it.",
+                font_res,
+            );
             if theme_overrides_back {
                 // The active theme provides its own back; the legacy
                 // picker has no visible effect, so we replace its