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_data/src/settings.rs

@@ -62,6 +62,21 @@ pub enum SyncBackend {
     },
 }
 
+/// Touch input mode — controls what a single tap on a face-up card does.
+///
+/// Defaults to `OneTap` so existing behaviour is unchanged on upgrade.
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize, Default)]
+pub enum TouchInputMode {
+    /// A single tap immediately moves the card to its best destination
+    /// (foundation-first, then tableau). This is the original behaviour.
+    #[default]
+    OneTap,
+    /// A first tap *selects* the card/stack and highlights it; a second
+    /// tap on a valid destination pile performs the move. Tapping the
+    /// selection again, or an empty / invalid target, cancels without moving.
+    TapToSelect,
+}
+
 /// Persisted window size (in logical pixels) and screen position
 /// (top-left corner, in physical pixels) — restored on next launch.
 ///
@@ -264,6 +279,13 @@ pub struct Settings {
     /// Defaults to `1` (the first site created in a fresh Matomo install).
     #[serde(default = "default_matomo_site_id")]
     pub matomo_site_id: u32,
+    /// Touch input mode — `OneTap` (default) auto-moves on first tap;
+    /// `TapToSelect` requires an explicit destination tap. Only affects
+    /// touch/Android; desktop mouse input is unchanged. Older
+    /// `settings.json` files deserialize cleanly to `OneTap` via
+    /// `#[serde(default)]`.
+    #[serde(default)]
+    pub touch_input_mode: TouchInputMode,
 }
 
 fn default_draw_mode() -> DrawMode {
@@ -397,6 +419,7 @@ impl Default for Settings {
             analytics_enabled: false,
             matomo_url: None,
             matomo_site_id: default_matomo_site_id(),
+            touch_input_mode: TouchInputMode::OneTap,
         }
     }
 }