fix: sync global theme on construct when theme option is explicitly provided

src/core.js

@@ -11,7 +11,7 @@ import { injectStyles } from './styles.js';
 import { t as i18nT, getCurrentLocale, getLocaleDirection } from './i18n.js';
 import { parseMarkdown } from './parser.js';
 import { presetPlugins } from './plugins.js';
-import { getTheme } from './themes.js';
+import { getTheme, applyTheme, saveTheme } from './themes.js';
 
 const MODES = ['edit', 'split', 'preview'];
 
@@ -97,6 +97,13 @@ class MarkdownEditor {
 
     injectStyles();
     this._buildDOM();
+
+    // 主题同步：用户显式传 theme 时覆盖全局 CSS 变量并持久化，否则尊重 localStorage
+    if (options.theme) {
+      applyTheme(this.config.theme);
+      saveTheme(this.config.theme);
+    }
+
     this._buildToolbar();
     this._bindEvents();