fix(engine): single-card double-click with no destination now plays the reject animation

handle_double_click had a coverage gap. The flow was:

  - Priority 1: try moving the single top card to its best
    destination (foundation, then tableau).
  - Priority 2: if Priority 1 failed AND the player clicked the
    base of a multi-card stack, try moving the whole stack.

`MoveRejectedEvent` was only fired inside the Priority 2 else-branch
— so a double-click on a single card with no legal destination
fell through both priorities silently: no card_invalid.wav, no
shake animation on the source pile, the player got zero feedback
that the click was acknowledged.

The fix collapses both priorities' failure paths into one
unconditional `MoveRejectedEvent` write at the end of the
double-click branch. Single-card miss now plays the same feedback
as multi-card-stack miss. The early `return` on each successful
move keeps the rejection branch from firing on the success path.

Pre-fix, a player double-clicking the 7♠ buried under a 6♥ on
column 5 (no foundation slot for 7s; no tableau column accepting
black 7) saw nothing happen. Post-fix, the source pile shakes
and the invalid-move sound plays, exactly like a drag-and-drop
rejection.

Workspace: 1170 passing tests / 0 failing. cargo clippy
--workspace --all-targets -- -D warnings clean.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

solitaire_engine/src/input_plugin.rs

@@ -1310,32 +1310,37 @@ fn handle_double_click(
         // Priority 2: if the player clicked the base of a multi-card face-up
         // stack (card_ids.len() > 1), try moving the whole stack to another
         // tableau column.
-        if card_ids.len() > 1 {
-            let Some(bottom_card) = game.0.piles.get(&pile)
-                .and_then(|p| p.cards.get(stack_index)) else { return };
-            if let Some((dest, count)) = best_tableau_destination_for_stack(
+        if card_ids.len() > 1
+            && let Some(bottom_card) = game.0.piles.get(&pile)
+                .and_then(|p| p.cards.get(stack_index))
+            && let Some((dest, count)) = best_tableau_destination_for_stack(
                 bottom_card,
                 &pile,
                 &game.0,
                 card_ids.len(),
-            ) {
+            )
+        {
             moves.write(MoveRequestEvent {
                 from: pile,
                 to: dest,
                 count,
             });
-            } else {
-                // No legal destination for the stack — play the invalid-move
-                // sound and shake the source pile cards as feedback.
-                // `MoveRejectedEvent` with `from == to` routes the shake to
-                // the source pile (which `start_shake_anim` reads from `ev.to`).
+            return;
+        }
+
+        // Both priorities failed — play the invalid-move sound and shake
+        // the source pile as feedback. `MoveRejectedEvent` with
+        // `from == to` routes the shake to the source pile (which
+        // `start_shake_anim` reads from `ev.to`). Pre-fix, this branch
+        // only fired for multi-card stacks, so a double-click on a
+        // single card with no legal destination did nothing — no
+        // sound, no shake. Now both single-card and stack misses get
+        // the same feedback.
         rejected.write(MoveRejectedEvent {
             from: pile.clone(),
             to: pile,
             count: card_ids.len(),
         });
-            }
-        }
     } else {
         // Single click — record the time.
         last_click.insert(top_card_id, now);