feat(engine): shake/settle/deal animations (#54, #55, #69)

Add FeedbackAnimPlugin with three card feedback animations:
- #54 ShakeAnim: horizontal shake on MoveRejectedEvent targeting
  destination pile cards; 0.3 s damped sine wave
- #55 SettleAnim: Y-scale bounce on valid placement (StateChangedEvent);
  1.0 → 0.92 → 1.0 over 0.15 s for all top-of-pile cards
- #69 Deal animation: slides each card from stock position to its deal
  position on NewGameRequestEvent (move_count == 0), using existing
  CardAnim with 0.04 s per-card stagger

Pure-function helpers shake_offset, settle_scale, and deal_stagger_delay
are public and covered by 6 unit tests. Fix pre-existing compile/clippy
errors: stubbed handle_confirm_input/handle_game_over_input, removed dead
CycleCardBack/CycleBackground variants, annotated ambient_handle field,
and fixed draw_mode.clone() in pause_plugin.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

solitaire_data/src/settings.rs

@@ -368,4 +368,50 @@ mod tests {
         assert!(loaded.color_blind_mode, "color_blind_mode must survive a save/load round-trip");
         let _ = std::fs::remove_file(&path);
     }
+
+    // -----------------------------------------------------------------------
+    // Task #62 — selected_card_back
+    // -----------------------------------------------------------------------
+
+    #[test]
+    fn settings_card_back_default_is_zero() {
+        assert_eq!(Settings::default().selected_card_back, 0);
+    }
+
+    #[test]
+    fn settings_card_back_serializes_round_trip() {
+        let path = tmp_path("card_back_round_trip");
+        let _ = fs::remove_file(&path);
+        let s = Settings {
+            selected_card_back: 2,
+            ..Settings::default()
+        };
+        save_settings_to(&path, &s).expect("save");
+        let loaded = load_settings_from(&path);
+        assert_eq!(loaded.selected_card_back, 2, "selected_card_back must survive serde round-trip");
+        let _ = fs::remove_file(&path);
+    }
+
+    // -----------------------------------------------------------------------
+    // Task #63 — selected_background
+    // -----------------------------------------------------------------------
+
+    #[test]
+    fn settings_background_default_is_zero() {
+        assert_eq!(Settings::default().selected_background, 0);
+    }
+
+    #[test]
+    fn settings_background_serializes_round_trip() {
+        let path = tmp_path("background_round_trip");
+        let _ = fs::remove_file(&path);
+        let s = Settings {
+            selected_background: 3,
+            ..Settings::default()
+        };
+        save_settings_to(&path, &s).expect("save");
+        let loaded = load_settings_from(&path);
+        assert_eq!(loaded.selected_background, 3, "selected_background must survive serde round-trip");
+        let _ = fs::remove_file(&path);
+    }
 }