refactor(core): 拆分 4 模块 + 插件状态 Symbol 化 + eslint type-aware

- core.ts 从 1162 行降至 865 行：命令/浮动工具栏/右键菜单/大纲
  拆至 commands.ts / floating-toolbar.ts / context-menu.ts / outline.ts
  （原型安装，API 与测试完全兼容）
- 6 个预设插件状态改用 Symbol 键存储，定义 EditorLike 契约接口，
  消灭 (editor as any).__xxx 魔法属性
- 实现 maxLength（textarea maxlength + 程序化入口截断）与
  zenMode 初始状态（此前为 dead config）
- 搜索面板补齐 matchCase/wholeWord（翻译键已有但未实现，
  中文全字边界感知）
- 分隔条 localStorage key 加入实例 id 隔离
- eslint 启用 type-aware 规则（consistent-type-imports /
  no-unnecessary-type-assertion），0 errors

tests/core.test.ts

@@ -2301,3 +2301,116 @@ describe('MarkdownEditor - v0.2.3 getStatus', () => {
     ed.destroy();
   });
 });
+
+// ============ v0.2.5 maxLength / zenMode / 分隔条隔离 ============
+
+describe('MarkdownEditor - v0.2.5 maxLength', () => {
+  test('setValue 超长内容被截断', () => {
+    document.body.innerHTML = '';
+    const c = document.createElement('div');
+    document.body.appendChild(c);
+    const ed = new MarkdownEditor(c, { maxLength: 10 });
+    ed.setValue('0123456789ABC');
+    expect(ed.getValue()).toBe('0123456789');
+    expect(ed.textarea.value).toBe('0123456789');
+    ed.destroy();
+  });
+
+  test('insert 超长内容被截断', () => {
+    document.body.innerHTML = '';
+    const c = document.createElement('div');
+    document.body.appendChild(c);
+    const ed = new MarkdownEditor(c, { maxLength: 5, value: 'ab' });
+    ed.focus();
+    ed.textarea.setSelectionRange(2, 2);
+    ed.insert('CDEFG');
+    expect(ed.getValue()).toBe('abCDE');
+    ed.destroy();
+  });
+
+  test('textarea maxlength 属性已绑定', () => {
+    document.body.innerHTML = '';
+    const c = document.createElement('div');
+    document.body.appendChild(c);
+    const ed = new MarkdownEditor(c, { maxLength: 42 });
+    expect(ed.textarea.maxLength).toBe(42);
+    ed.destroy();
+  });
+
+  test('maxLength 为 0 时不限制', () => {
+    document.body.innerHTML = '';
+    const c = document.createElement('div');
+    document.body.appendChild(c);
+    const ed = new MarkdownEditor(c, {});
+    expect(ed.textarea.maxLength).toBe(-1);
+    const long = 'x'.repeat(10000);
+    ed.setValue(long);
+    expect(ed.getValue().length).toBe(10000);
+    ed.destroy();
+  });
+});
+
+describe('MarkdownEditor - v0.2.5 zenMode 初始状态', () => {
+  test('zenMode: true 启动即进入 Zen 模式', () => {
+    document.body.innerHTML = '';
+    const c = document.createElement('div');
+    document.body.appendChild(c);
+    const ed = new MarkdownEditor(c, { zenMode: true });
+    expect(ed.isZen()).toBe(true);
+    expect(ed.el.classList.contains('me-zen')).toBe(true);
+    expect(ed.toolbarEl.style.opacity).toBe('0');
+    ed.destroy();
+  });
+
+  test('默认不进入 Zen 模式', () => {
+    document.body.innerHTML = '';
+    const c = document.createElement('div');
+    document.body.appendChild(c);
+    const ed = new MarkdownEditor(c, {});
+    expect(ed.isZen()).toBe(false);
+    expect(ed.el.classList.contains('me-zen')).toBe(false);
+    ed.destroy();
+  });
+
+  test('zenMode 初始开启后 toggleZen 可关闭', () => {
+    document.body.innerHTML = '';
+    const c = document.createElement('div');
+    document.body.appendChild(c);
+    const ed = new MarkdownEditor(c, { zenMode: true });
+    ed.toggleZen();
+    expect(ed.isZen()).toBe(false);
+    expect(ed.el.classList.contains('me-zen')).toBe(false);
+    ed.destroy();
+  });
+});
+
+describe('MarkdownEditor - v0.2.5 分隔条实例隔离', () => {
+  test('分隔条位置按实例 id 保存', () => {
+    localStorage.clear();
+    document.body.innerHTML = '';
+    const c = document.createElement('div');
+    document.body.appendChild(c);
+    const ed = new MarkdownEditor(c, { id: 'divider-test-1' });
+    ed.editorPane.style.flex = '0 0 30%';
+    ed._saveDividerPosition();
+    expect(localStorage.getItem('metona-editor-divider-divider-test-1')).toBe('0 0 30%');
+    expect(localStorage.getItem('metona-editor-divider')).toBeNull();
+    ed.destroy();
+  });
+
+  test('不同实例互不覆盖分隔条位置', () => {
+    localStorage.clear();
+    document.body.innerHTML = '';
+    const c = document.createElement('div');
+    document.body.appendChild(c);
+    const a = new MarkdownEditor(c, { id: 'dva' });
+    const b = new MarkdownEditor(c, { id: 'dvb' });
+    a.editorPane.style.flex = '0 0 20%';
+    b.editorPane.style.flex = '0 0 70%';
+    a._saveDividerPosition();
+    b._saveDividerPosition();
+    expect(localStorage.getItem('metona-editor-divider-dva')).toBe('0 0 20%');
+    expect(localStorage.getItem('metona-editor-divider-dvb')).toBe('0 0 70%');
+    a.destroy(); b.destroy();
+  });
+});