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/sync_plugin.rs

@@ -101,7 +101,6 @@ impl SyncPlugin {
 impl Plugin for SyncPlugin {
     fn build(&self, app: &mut App) {
         app.insert_resource(SyncProviderResource(self.provider.clone()))
-            .init_resource::<TokioRuntimeResource>()
             .init_resource::<SyncStatusResource>()
             .init_resource::<PullTaskResult>()
             .init_resource::<PullTask>()
@@ -109,18 +108,30 @@ impl Plugin for SyncPlugin {
             .add_message::<ManualSyncRequestEvent>()
             .add_message::<SyncCompleteEvent>()
             .add_message::<SyncConfigureRequestEvent>()
-            .add_message::<WarningToastEvent>()
-            .add_systems(Startup, start_pull)
-            .add_systems(
-                Update,
-                (
-                    poll_pull_result,
-                    handle_manual_sync_request,
-                    push_replay_on_win,
-                    poll_replay_upload_result,
-                ),
-            )
-            .add_systems(Last, push_on_exit);
+            .add_message::<WarningToastEvent>();
+
+        // Build the shared Tokio runtime; disable all network sync if the OS
+        // refuses to create threads (resource-limited environments, sandboxed
+        // Android builds, etc.).
+        match TokioRuntimeResource::new() {
+            Ok(rt) => {
+                app.insert_resource(rt)
+                    .add_systems(Startup, start_pull)
+                    .add_systems(
+                        Update,
+                        (
+                            poll_pull_result,
+                            handle_manual_sync_request,
+                            push_replay_on_win,
+                            poll_replay_upload_result,
+                        ),
+                    )
+                    .add_systems(Last, push_on_exit);
+            }
+            Err(e) => {
+                warn!("sync: failed to create Tokio runtime — network sync disabled: {e}");
+            }
+        }
     }
 }