fix(multi): resolve 26 bugs found in comprehensive codebase review

Core fixes (issues #12, #13, #22):
- #12: undo now preserves score delta instead of restoring snapshot score
- #13: take_from_foundation defaults to false (non-standard house rule)
- #22: check_win validates full suit sequence, not just card count

Engine fixes:
- #8:  replay keyboard input guard against non-replay state
- #9:  help modal scrims.is_empty() guard added
- #10: settings modal scrims.is_empty() guard added
- #11: sync_plugin builds payload at poll time (not task-spawn time)
- #14: server replay mode case-sensitivity fix ("Classic")
- #15: play_by_seed_plugin confirmed flag set to true on launch
- #16: replay back-step debounce via Local<bool> + StateChangedEvent;
       register StateChangedEvent in ReplayOverlayPlugin (fixes 52 tests)
- #17: time-attack timer ignores win-summary overlay
- #18: HUD dropdown glyphs U+25BE → U+2193 (FiraMono-safe arrow)
- #19: theme plugin applies immediate visual update on A→B→A switch
- #20: SyncAuthError / SyncBusyOverlay split into separate entities so
       auth errors are visible after busy overlay is hidden
- #21: handle_forfeit ordered before update_stats_on_new_game
- #23: server merge uses correct avg_time_seconds and games_lost math
- #24: win_summary migrated to ModalScrim pattern
- #25: card_animation apply_deferred between animation systems
- #26: cursor_plugin HashMap access uses .get() with fallback
- #27: auto_complete mid-sequence deactivation guard
- #28: feedback_anim SettleAnim ordered before FoundationFlourish
- #29: achievement_plugin iterates all win events; adds scrims guard
- #30: leaderboard modal scrims.is_empty() guard added
- #31: server auth tmp file cleanup on rename failure
- #32: sync_setup modal scrims.is_empty() guard added
- #33: font_plugin uses match fallback; TokioRuntimeResource graceful
       current-thread fallback on runtime init failure

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

solitaire_engine/src/input_plugin.rs

@@ -47,6 +47,7 @@ use crate::game_plugin::{ConfirmNewGameScreen, GameMutation, RestorePromptScreen
 use crate::pause_plugin::PausedResource;
 use crate::progress_plugin::ProgressResource;
 use crate::layout::{Layout, LayoutResource};
+use crate::replay_playback::ReplayPlaybackState;
 use crate::resources::{DragState, GameInputConsumedResource, GameStateResource, HintCycleIndex};
 use crate::selection_plugin::SelectionState;
 use crate::time_attack_plugin::TimeAttackResource;
@@ -175,11 +176,20 @@ fn handle_keyboard_core(
     mut zen_requests: MessageReader<StartZenRequestEvent>,
     confirm_screens: Query<(), With<ConfirmNewGameScreen>>,
     restore_prompts: Query<(), With<RestorePromptScreen>>,
+    replay_state: Option<Res<ReplayPlaybackState>>,
 ) {
     if paused.is_some_and(|p| p.0) {
         return;
     }
 
+    // During replay playback (Playing or Completed) all game-input shortcuts
+    // are suppressed. The replay overlay owns Space (pause/resume) and the
+    // arrow keys (step). Letting game input through would mutate
+    // `GameStateResource` and corrupt replay determinism.
+    if replay_state.is_some_and(|r| !matches!(*r, ReplayPlaybackState::Inactive)) {
+        return;
+    }
+
     if keys.just_pressed(KeyCode::KeyU) {
         ev.undo.write(UndoRequestEvent);
     }