feat: read local theme on page load (#1114)

Co-authored-by: zqran <uuxnet@gmail.com>

packages/component/src/styles/utils/localStorageThemeHelper.ts

@@ -2,11 +2,13 @@ import { ThemeMode } from '../types';
 
 export class LocalStorageThemeHelper {
   name = 'Affine-theme-mode';
+  callback = new Set<() => void>();
   get = (): ThemeMode | null => {
     return localStorage.getItem(this.name) as ThemeMode | null;
   };
   set = (mode: ThemeMode) => {
     localStorage.setItem(this.name, mode);
+    this.callback.forEach(cb => cb());
   };
 }