feat(settings_sync): add syncing with store

src/svelte-interface/hooks/ThemeUpdates.ts

@@ -0,0 +1,29 @@
+type ThemeUpdateCallback = () => void;
+
+class ThemeUpdates {
+  private static instance: ThemeUpdates;
+  private listeners: Set<ThemeUpdateCallback> = new Set();
+
+  private constructor() {}
+
+  public static getInstance(): ThemeUpdates {
+    if (!ThemeUpdates.instance) {
+      ThemeUpdates.instance = new ThemeUpdates();
+    }
+    return ThemeUpdates.instance;
+  }
+
+  public addListener(callback: ThemeUpdateCallback): void {
+    this.listeners.add(callback);
+  }
+
+  public removeListener(callback: ThemeUpdateCallback): void {
+    this.listeners.delete(callback);
+  }
+
+  public triggerUpdate(): void {
+    this.listeners.forEach(callback => callback());
+  }
+}
+
+export const themeUpdates = ThemeUpdates.getInstance();