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_engine/src/lib.rs

@@ -1,9 +1,6 @@
 //! Bevy integration layer for Solitaire Quest.
-//!
-//! Currently exposes `GamePlugin` plus the resources and events it owns.
-//! Additional plugins (`TablePlugin`, `CardPlugin`, `InputPlugin`,
-//! `AnimationPlugin`, etc.) land in later sub-phases of Phase 3.
 
+pub mod animation_plugin;
 pub mod card_plugin;
 pub mod events;
 pub mod game_plugin;
@@ -12,10 +9,11 @@ pub mod layout;
 pub mod resources;
 pub mod table_plugin;
 
+pub use animation_plugin::{AnimationPlugin, CardAnim};
 pub use card_plugin::{CardEntity, CardLabel, CardPlugin};
 pub use events::{
-    CardFlippedEvent, DrawRequestEvent, GameWonEvent, MoveRequestEvent, NewGameRequestEvent,
-    StateChangedEvent, UndoRequestEvent,
+    AchievementUnlockedEvent, CardFlippedEvent, DrawRequestEvent, GameWonEvent, MoveRequestEvent,
+    NewGameRequestEvent, StateChangedEvent, UndoRequestEvent,
 };
 pub use game_plugin::{GameMutation, GamePlugin};
 pub use input_plugin::InputPlugin;