style: simplify button labels (drop emoji, keep text)

- 🪄 AI 智能编辑 → AI
- 🚀 发送 → 发送
- ✕ 取消 → 取消

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/components/opencode_cell_actions.ts

@@ -88,7 +88,7 @@ export class OpenCodeCellActions extends Widget {
 
     const btn = document.createElement('button');
     btn.className = 'opencode-btn opencode-btn-ai';
-    btn.textContent = '🪄 AI 智能编辑';
+    btn.textContent = 'AI';
     btn.disabled = baseDisabled;
     btn.title = baseDisabled
       ? 'OpenCode: 等待 cell 上下文…'