perf: 优化浮动工具栏 selectionChange 轮询间隔 200ms→500ms，修复测试缓慢问题

src/core.ts

@@ -747,33 +747,33 @@ export class MarkdownEditor {
 
     const hide = () => { this._hideFloatingToolbar(); };
 
-    // Detect selection changes
-    ta.addEventListener('mouseup', () => setTimeout(show, 0));
-    ta.addEventListener('keyup', () => {
-      if (ta.selectionStart !== ta.selectionEnd) setTimeout(show, 0);
-      else setTimeout(hide, 0);
-      // Emit cursorMove
-      const pos = this.getCursorPosition();
-      this._emit('cursorMove', pos);
-    });
-    ta.addEventListener('blur', () => setTimeout(hide, 300));
-    ta.addEventListener('click', () => setTimeout(() => {
-      if (ta.selectionStart === ta.selectionEnd) hide();
-    }, 0));
-
-    // Emit selectionChange on selection changes
+    // Detect selection changes via events + throttled polling
     let lastSelStart = ta.selectionStart;
     let lastSelEnd = ta.selectionEnd;
-    this._selectionTimer = setInterval(() => {
-      if (this._destroyed) return;
+    const check = () => {
+      if (this._destroyed || !document.body.contains(ta)) return;
       const s = ta.selectionStart; const e = ta.selectionEnd;
       if (s !== lastSelStart || e !== lastSelEnd) {
         lastSelStart = s; lastSelEnd = e;
         const text = this._value.slice(s, e);
         this._emit('selectionChange', { start: s, end: e, text });
       }
-    }, 200) as any;
-    this._cleanups.push(() => { if (this._selectionTimer) clearInterval(this._selectionTimer); });
+    };
+    // Use longer interval for polling (won't block event loop as much)
+    this._selectionTimer = setInterval(check, 500) as any;
+    this._cleanups.push(() => { if (this._selectionTimer) { clearInterval(this._selectionTimer); this._selectionTimer = null; } });
+
+    ta.addEventListener('mouseup', () => setTimeout(show, 0));
+    ta.addEventListener('keyup', () => {
+      const s = ta.selectionStart; const e = ta.selectionEnd;
+      if (s !== e) setTimeout(show, 0);
+      else setTimeout(hide, 0);
+      this._emit('cursorMove', this.getCursorPosition());
+    });
+    ta.addEventListener('blur', () => setTimeout(hide, 300));
+    ta.addEventListener('click', () => setTimeout(() => {
+      if (ta.selectionStart === ta.selectionEnd) hide();
+    }, 0));
   }
 
   _buildFloatingToolbar(): void {