feat(engine): add AnimationPlugin with slide, cascade, and toast (Phase 3F)

- CardAnim component lerps cards from old to new position on every move
- card_plugin now adds CardAnim instead of teleporting cards on state change
- Snap-back on invalid drag reuses the same mechanism (StateChangedEvent)
- Win cascade flies all 52 cards off-screen with staggered delay on GameWonEvent
- Achievement toast scaffold wired to AchievementUnlockedEvent (Phase 5 content)
- Fix input_plugin test: click Queen's visible strip, not geometric centre

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

solitaire_app/src/main.rs

@@ -1,5 +1,5 @@
 use bevy::prelude::*;
-use solitaire_engine::{CardPlugin, GamePlugin, InputPlugin, TablePlugin};
+use solitaire_engine::{AnimationPlugin, CardPlugin, GamePlugin, InputPlugin, TablePlugin};
 
 fn main() {
     App::new()
@@ -17,5 +17,6 @@ fn main() {
         .add_plugins(TablePlugin)
         .add_plugins(CardPlugin)
         .add_plugins(InputPlugin)
+        .add_plugins(AnimationPlugin)
         .run();
 }