fix: 移除 setInterval 轮询，改用纯事件驱动 selectionChange — 修复 CI 卡死问题

tests/core.test.ts

@@ -2179,13 +2179,10 @@ describe('MarkdownEditor - v0.2.3 浮动工具栏', () => {
     const c = document.createElement('div');
     document.body.appendChild(c);
     const ed = new MarkdownEditor(c, { value: 'hello world' });
-    // 浮动工具栏应被注入 CSS
     const style = document.getElementById('me-float-style');
     expect(style).not.toBeNull();
-    // _floatingToolbar 在首次 selection 时才创建 DOM
     expect(ed._floatingToolbar).toBeNull();
-    // _selectionTimer 已启动
-    expect(ed._selectionTimer).not.toBeNull();
+    expect(ed._floatingEnabled).toBe(true);
     ed.destroy();
   });
 
@@ -2194,8 +2191,7 @@ describe('MarkdownEditor - v0.2.3 浮动工具栏', () => {
     const c = document.createElement('div');
     document.body.appendChild(c);
     const ed = new MarkdownEditor(c, { value: 'hello', floatingToolbar: false });
-    // 浮动工具栏应不启动（_selectionTimer 为 null）
-    expect(ed._selectionTimer).toBeNull();
+    expect(ed._floatingEnabled).toBe(false);
     expect(ed._floatingToolbar).toBeNull();
     ed.destroy();
   });
@@ -2224,26 +2220,23 @@ describe('MarkdownEditor - v0.2.3 浮动工具栏', () => {
     expect(ed._floatingToolbar).not.toBeNull();
     ed.destroy();
     expect(ed._floatingToolbar).toBeNull();
-    expect(ed._selectionTimer).toBeNull();
   });
 
-  test('selectionChange 事件触发', (done) => {
+  test('selectionChange 事件触发', () => {
     document.body.innerHTML = '';
     const c = document.createElement('div');
     document.body.appendChild(c);
     const ed = new MarkdownEditor(c, { value: 'hello world' });
     const handler = jest.fn();
     ed.on('selectionChange', handler);
+    // Fire keyup after setting selection — selectionChange is emitted synchronously in the handler
     ed.textarea.setSelectionRange(0, 5);
-    // selectionChange 通过 interval 检测，等 300ms
-    setTimeout(() => {
-      expect(handler).toHaveBeenCalled();
-      expect(handler.mock.calls[0][0]).toHaveProperty('start', 0);
-      expect(handler.mock.calls[0][0]).toHaveProperty('end', 5);
-      expect(handler.mock.calls[0][0]).toHaveProperty('text', 'hello');
-      ed.destroy();
-      done();
-    }, 800);
+    ed.textarea.dispatchEvent(new KeyboardEvent('keyup', { key: 'ArrowRight', bubbles: true }));
+    expect(handler).toHaveBeenCalled();
+    expect(handler.mock.calls[0][0]).toHaveProperty('start', 0);
+    expect(handler.mock.calls[0][0]).toHaveProperty('end', 5);
+    expect(handler.mock.calls[0][0]).toHaveProperty('text', 'hello');
+    ed.destroy();
   });
 
   test('cursorMove 事件在按键后触发', () => {