feat(toast): wire ToastVariant::Error for invalid-move feedback

Resume-prompt Option C — first in-engine consumer of
`ToastVariant::Error`. The variant has had a slot in the enum
since v0.20.0's toast system landed; this commit wires a real
driver event so the slot is no longer dead code.

### Driver: MoveRejectedEvent

When a player tries an illegal placement (drops dragged cards on
a real pile but the move violates the rules), `MoveRejectedEvent`
fires. The existing rejection-feedback chain plays
`card_invalid.wav` (audio cue) and triggers the destination-pile
shake (visual cue via `feedback_anim_plugin`). This commit adds a
third leg — a 2-second pink-bordered Error toast reading
"Invalid move" — primarily for accessibility:

- **Audio cue alone** doesn't help deaf players.
- **Visual shake alone** is brief and easy to miss for low-vision
  players or anyone with reduce-motion enabled (which gates the
  shake's animation timing).
- **Toast text** is persistent ~2 s, readable, and unambiguous.

The three legs together cover the major perception channels.

### Implementation

New `handle_move_rejected_toast` system in `animation_plugin`
mirrors the shape of `handle_xp_awarded_toast` — read events,
fire `spawn_toast(commands, "Invalid move", 2.0,
ToastVariant::Error)`. Registered in the plugin's Update set
between `handle_xp_awarded_toast` and `tick_toasts` so the toast
spawn pipeline picks it up the same frame the event fires.

`AnimationPlugin::build` gains
`.add_message::<MoveRejectedEvent>()` so the message is
initialized when the plugin runs under MinimalPlugins (tests).
The message is also registered by `feedback_anim_plugin` —
Bevy's `add_message` is idempotent, so both registrations
coexist cleanly.

Also drops the `#[allow(dead_code)]` from `ToastVariant::Error`
(stale now that the variant has a real consumer) and updates the
variant's doc comment to point at `handle_move_rejected_toast`.

### Test

New `move_rejected_event_spawns_error_toast` pins the wiring:
firing a `MoveRejectedEvent` spawns exactly one `ToastOverlay`
on the next tick. Matches the shape of the existing
`info_toast_event_spawns_toast_overlay` test. 1195 passing
(+1 from prior 1194).

Workspace clippy clean.

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

solitaire_engine/src/animation_plugin.rs

@@ -21,8 +21,9 @@ use crate::card_animation::{sample_curve, CardAnimation, MotionCurve};
 use crate::card_plugin::CardEntity;
 use crate::challenge_plugin::ChallengeAdvancedEvent;
 use crate::daily_challenge_plugin::{DailyChallengeCompletedEvent, DailyGoalAnnouncementEvent};
-use crate::events::{InfoToastEvent, XpAwardedEvent};
-use crate::events::{AchievementUnlockedEvent, GameWonEvent};
+use crate::events::{
+    AchievementUnlockedEvent, GameWonEvent, InfoToastEvent, MoveRejectedEvent, XpAwardedEvent,
+};
 use crate::game_plugin::GameMutation;
 use crate::layout::LayoutResource;
 use crate::pause_plugin::PausedResource;
@@ -162,6 +163,7 @@ impl Plugin for AnimationPlugin {
             .add_message::<ChallengeAdvancedEvent>()
             .add_message::<SettingsChangedEvent>()
             .add_message::<InfoToastEvent>()
+            .add_message::<MoveRejectedEvent>()
             .add_message::<XpAwardedEvent>()
             .init_resource::<EffectiveSlideDuration>()
             .init_resource::<ToastQueue>()
@@ -183,6 +185,7 @@ impl Plugin for AnimationPlugin {
                     handle_settings_toast,
                     handle_auto_complete_toast,
                     handle_xp_awarded_toast,
+                    handle_move_rejected_toast,
                     tick_toasts,
                     (enqueue_toasts, drive_toast_display).chain(),
                 )
@@ -565,9 +568,11 @@ pub enum ToastVariant {
     /// event; kept so future warning-flavoured toasts have a slot.
     #[allow(dead_code)]
     Warning,
-    /// Failure / rejected action — pink border. Currently unused; kept so
-    /// future error-flavoured toasts have a slot.
-    #[allow(dead_code)]
+    /// Failure / rejected action — pink border. Used by
+    /// [`handle_move_rejected_toast`] for illegal-placement
+    /// feedback; the third leg of the rejection-feedback stool
+    /// alongside `card_invalid.wav` (audio) and the destination-
+    /// pile shake (visual).
     Error,
     /// Reward / milestone — lavender border. Used for XP awards,
     /// achievement unlocks, level-ups, daily/weekly/challenge completions.
@@ -622,6 +627,30 @@ fn handle_xp_awarded_toast(mut commands: Commands, mut events: MessageReader<XpA
     }
 }
 
+/// Spawns a 2-second pink-bordered Error toast when the player tries an
+/// illegal placement (`MoveRejectedEvent`). Adds a third leg to the
+/// existing rejection feedback stool — `card_invalid.wav` already plays
+/// (audio cue) and `feedback_anim_plugin::queue_shake_for_rejected_move`
+/// fires the destination-pile shake (visual cue). The toast is the
+/// accessibility-focused leg: persistent ~2 s text that's readable for
+/// deaf players and impossible to miss for players who blink during the
+/// shake. First in-engine consumer of `ToastVariant::Error` — exercises
+/// the variant's pink border accent and the design-system "rejected
+/// action" semantic.
+fn handle_move_rejected_toast(
+    mut commands: Commands,
+    mut events: MessageReader<MoveRejectedEvent>,
+) {
+    for _ev in events.read() {
+        spawn_toast(
+            &mut commands,
+            "Invalid move".to_string(),
+            2.0,
+            ToastVariant::Error,
+        );
+    }
+}
+
 /// Ticks down `ToastTimer` on each toast and despawns it when the timer expires.
 ///
 /// Skipped while the game is paused so toast countdowns freeze along with the
@@ -966,6 +995,44 @@ mod tests {
         let _ = count;
     }
 
+    #[test]
+    fn move_rejected_event_spawns_error_toast() {
+        // The first in-engine consumer of `ToastVariant::Error`. Firing
+        // a `MoveRejectedEvent` (illegal placement) must spawn exactly
+        // one `ToastOverlay` carrying the rejection-feedback message.
+        // Pairs the existing audio (`card_invalid.wav`) and visual
+        // (`feedback_anim_plugin::queue_shake_for_rejected_move`) feedback
+        // with an accessibility-focused readable text cue.
+        use solitaire_core::pile::PileType;
+        let mut app = App::new();
+        app.add_plugins(MinimalPlugins).add_plugins(AnimationPlugin);
+
+        // Baseline: no toast overlays exist before the event.
+        let before = app
+            .world_mut()
+            .query::<&ToastOverlay>()
+            .iter(app.world())
+            .count();
+
+        app.world_mut().write_message(MoveRejectedEvent {
+            from: PileType::Tableau(0),
+            to: PileType::Tableau(1),
+            count: 1,
+        });
+        app.update();
+
+        let after = app
+            .world_mut()
+            .query::<&ToastOverlay>()
+            .iter(app.world())
+            .count();
+        assert_eq!(
+            after,
+            before + 1,
+            "MoveRejectedEvent must spawn exactly one error toast",
+        );
+    }
+
     // -----------------------------------------------------------------------
     // Task #67 — Toast queue pure-function tests
     // -----------------------------------------------------------------------