feat(toast): wire ToastVariant::Warning for daily-challenge expiry

Adds the first in-engine consumer of `ToastVariant::Warning` — a 4s
amber-bordered toast that fires once per daily-challenge date when the
player is within 30 minutes of UTC midnight reset and hasn't yet
completed today's challenge.

Mirrors the v0.21.2 `ToastVariant::Error` wiring: a domain-event
message (`WarningToastEvent(String)`) crosses the plugin boundary;
`animation_plugin::handle_warning_toast` reads it and spawns the
fire-and-forget toast. Suppression is decided by a pure helper
(`compute_expiry_warning_minutes`) that's exhaustively covered by 7
unit tests + 1 in-Bevy idempotence test.

After this lands, every `ToastVariant` (Info, Warning, Error,
Celebration) has at least one real driver — closing the "is this enum
scaffolding or load-bearing?" ambiguity that's been latent since the
variant was introduced.

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

solitaire_engine/src/animation_plugin.rs

@@ -22,7 +22,8 @@ use crate::card_plugin::CardEntity;
 use crate::challenge_plugin::ChallengeAdvancedEvent;
 use crate::daily_challenge_plugin::{DailyChallengeCompletedEvent, DailyGoalAnnouncementEvent};
 use crate::events::{
-    AchievementUnlockedEvent, GameWonEvent, InfoToastEvent, MoveRejectedEvent, XpAwardedEvent,
+    AchievementUnlockedEvent, GameWonEvent, InfoToastEvent, MoveRejectedEvent, WarningToastEvent,
+    XpAwardedEvent,
 };
 use crate::game_plugin::GameMutation;
 use crate::layout::LayoutResource;
@@ -164,6 +165,7 @@ impl Plugin for AnimationPlugin {
             .add_message::<SettingsChangedEvent>()
             .add_message::<InfoToastEvent>()
             .add_message::<MoveRejectedEvent>()
+            .add_message::<WarningToastEvent>()
             .add_message::<XpAwardedEvent>()
             .init_resource::<EffectiveSlideDuration>()
             .init_resource::<ToastQueue>()
@@ -186,6 +188,7 @@ impl Plugin for AnimationPlugin {
                     handle_auto_complete_toast,
                     handle_xp_awarded_toast,
                     handle_move_rejected_toast,
+                    handle_warning_toast,
                     tick_toasts,
                     (enqueue_toasts, drive_toast_display).chain(),
                 )
@@ -651,6 +654,23 @@ fn handle_move_rejected_toast(
     }
 }
 
+/// Spawns a 4-second amber-bordered Warning toast for every incoming
+/// [`WarningToastEvent`]. First in-engine consumer of
+/// [`ToastVariant::Warning`] — exercises the variant's amber accent and
+/// the design-system "act soon" semantic.
+///
+/// Mirrors [`handle_move_rejected_toast`] but reads a generic carrier
+/// event (not a domain-specific one) because Warning has multiple
+/// candidate drivers and the call-site knows the message wording.
+fn handle_warning_toast(
+    mut commands: Commands,
+    mut events: MessageReader<WarningToastEvent>,
+) {
+    for ev in events.read() {
+        spawn_toast(&mut commands, ev.0.clone(), 4.0, ToastVariant::Warning);
+    }
+}
+
 /// 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