feat(engine): reactive render — animations drive RequestRedraw, focused_mode reactive on Android

All per-frame animation tick systems now write MessageWriter<RequestRedraw>
each frame they have active work, allowing WinitSettings focused_mode to
switch from Continuous to reactive_low_power(100 ms) on Android.

Systems updated:
- advance_card_animations (CardAnimationPlugin)
- advance_card_anims (AnimationPlugin — deal/win cascade)
- tick_shake_anim, tick_settle_anim, tick_foundation_flourish (FeedbackAnimPlugin)
- drive_toast_display (AnimationPlugin — toast countdown)
- drive_auto_complete (AutoCompletePlugin — step interval keepalive)

The 100 ms low-power ceiling means the game timer still ticks ~10×/s
with no input; animations self-sustain via the redraw chain at full
frame rate while active; and the GPU is completely idle between frames
when the board is static.

Each plugin registers add_message::<RequestRedraw>() so the message
type is available under MinimalPlugins in unit tests.

Closes #78, #79

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

solitaire_app/src/lib.rs

@@ -172,13 +172,16 @@ fn build_app_with_settings(
     // a 1-second ceiling when the app is backgrounded cuts wake-up frequency
     // from ~60 Hz to ≤1 Hz, dramatically reducing background battery drain.
     //
-    // The focused mode stays Continuous so that card-slide animations remain
+    // focused_mode uses reactive_low_power(100 ms) so the CPU only wakes when
-    // smooth. PresentMode::AutoVsync (set above) keeps the GPU capped at the
+    // an event arrives (touch, resize, etc.) or an animation system writes
-    // display refresh rate (~60 Hz) when foregrounded, which already prevents
+    // RequestRedraw. The 100 ms ceiling is a fallback that ensures the game
-    // the GPU from spinning at 200+ fps between vsync intervals.
+    // timer ticks at least 10×/s even with no input, while keeping the GPU
+    // completely idle between frames when the board is static.
+    // PresentMode::AutoVsync (set above) still caps the GPU at the display
+    // refresh rate when frames do render.
     #[cfg(target_os = "android")]
     app.insert_resource(WinitSettings {
-        focused_mode: UpdateMode::Continuous,
+        focused_mode: UpdateMode::reactive_low_power(std::time::Duration::from_millis(100)),
         unfocused_mode: UpdateMode::reactive_low_power(std::time::Duration::from_secs(1)),
     });
 

solitaire_engine/src/animation_plugin.rs

@@ -13,6 +13,7 @@
 use std::collections::VecDeque;
 
 use bevy::prelude::*;
+use bevy::window::RequestRedraw;
 use solitaire_data::{AnimSpeed, Settings};
 
 use crate::achievement_plugin::display_name_for;
@@ -180,6 +181,7 @@ impl Plugin for AnimationPlugin {
             .add_message::<MoveRejectedEvent>()
             .add_message::<WarningToastEvent>()
             .add_message::<XpAwardedEvent>()
+            .add_message::<RequestRedraw>()
             .init_resource::<EffectiveSlideDuration>()
             .init_resource::<ToastQueue>()
             .init_resource::<ActiveToast>()

solitaire_engine/src/auto_complete_plugin.rs

@@ -9,6 +9,7 @@
 //! returns `None` (e.g. a transient state), the plugin retries next tick.
 
 use bevy::prelude::*;
+use bevy::window::RequestRedraw;
 
 use crate::audio_plugin::{AudioState, SoundLibrary};
 use crate::events::{MoveRequestEvent, StateChangedEvent};
@@ -39,7 +40,9 @@ pub struct AutoCompletePlugin;
 
 impl Plugin for AutoCompletePlugin {
     fn build(&self, app: &mut App) {
-        app.init_resource::<AutoCompleteState>().add_systems(
+        app.init_resource::<AutoCompleteState>()
+            .add_message::<RequestRedraw>()
+            .add_systems(
             Update,
             (
                 detect_auto_complete,

solitaire_engine/src/card_animation/mod.rs

@@ -92,6 +92,7 @@ pub use timing::{
 pub use tuning::{AnimationTuning, InputPlatform};
 
 use bevy::prelude::*;
+use bevy::window::RequestRedraw;
 
 use crate::card_plugin::CardEntity;
 use crate::events::{DrawRequestEvent, GameWonEvent, MoveRequestEvent, UndoRequestEvent};
@@ -125,6 +126,7 @@ impl Plugin for CardAnimationPlugin {
             .add_message::<DrawRequestEvent>()
             .add_message::<UndoRequestEvent>()
             .add_message::<GameWonEvent>()
+            .add_message::<RequestRedraw>()
             .init_resource::<DragState>()
             .init_resource::<HoverState>()
             .init_resource::<InputBuffer>()

solitaire_engine/src/feedback_anim_plugin.rs

@@ -42,6 +42,7 @@ use std::f32::consts::PI;
 use std::hash::{Hash, Hasher};
 
 use bevy::prelude::*;
+use bevy::window::RequestRedraw;
 use solitaire_core::pile::PileType;
 use solitaire_data::AnimSpeed;
 
@@ -204,6 +205,7 @@ impl Plugin for FeedbackAnimPlugin {
             .add_message::<MoveRejectedEvent>()
             .add_message::<NewGameRequestEvent>()
             .add_message::<FoundationCompletedEvent>()
+            .add_message::<RequestRedraw>()
             .add_systems(
                 Update,
                 (