fix(engine): auto-complete delay + right-click shake on no legal move

Closes #80: add AUTO_COMPLETE_INITIAL_DELAY (0.75 s) before the first
auto-complete move fires. Previously cooldown was 0.0, causing the
sequence to hijack the board the same frame the condition was met.

Closes #81: fire MoveRejectedEvent in radial_open_on_right_click when
the right-clicked card has no legal destinations, so the shake
animation and invalid-move sound play consistently on desktop/web.

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

solitaire_engine/src/auto_complete_plugin.rs

@@ -26,6 +26,12 @@ const AUTO_COMPLETE_CHIME_VOLUME: f64 = 0.5;
 /// Seconds between consecutive auto-complete moves.
 const STEP_INTERVAL: f32 = 0.12;
 
+/// Seconds to wait after detection before firing the first auto-complete move.
+///
+/// This pause gives the player a moment to register that the game is
+/// transitioning into auto-complete mode before cards start moving.
+const AUTO_COMPLETE_INITIAL_DELAY: f32 = 0.75;
+
 /// Tracks whether auto-complete is active and when the next move fires.
 #[derive(Resource, Default, Debug)]
 pub struct AutoCompleteState {
@@ -74,7 +80,7 @@ fn detect_auto_complete(
     }
     if game.0.is_auto_completable && !state.active {
         state.active = true;
-        state.cooldown = 0.0; // fire first move immediately
+        state.cooldown = AUTO_COMPLETE_INITIAL_DELAY;
     }
     // Intentionally no `else if !is_auto_completable` branch here.
     // Deactivating on every frame where `is_auto_completable` is false
@@ -210,6 +216,12 @@ mod tests {
         app.world_mut().resource_mut::<GameStateResource>().0 = nearly_won_state();
         app.world_mut().write_message(StateChangedEvent);
         app.update(); // detect runs, sets active
+
+        // Zero out the cooldown so drive fires on the next update regardless
+        // of the initial delay constant.
+        app.world_mut()
+            .resource_mut::<AutoCompleteState>()
+            .cooldown = 0.0;
         app.update(); // drive fires the move
 
         let events = app.world().resource::<Messages<MoveRequestEvent>>();