feat: add shortcuts feature for form submission (halo-dev#99)

支持通过键盘快捷键提交表单。

- macOS: ⌘ + Enter
- Linux / Windows: Ctrl + Enter

Fixes halo-dev#93 

```release-note
支持通过键盘快捷键提交表单。
```

packages/comment-widget/src/base-form.ts

@@ -109,6 +109,24 @@ export class BaseForm extends LitElement {
     }
   }
 
+  onKeydown(e: KeyboardEvent) {
+    if (e.key === 'Enter' && (e.metaKey || e.ctrlKey)) {
+      const form = this.shadowRoot?.querySelector('form');
+      e.preventDefault();
+      form?.requestSubmit();
+    }
+  }
+
+  override connectedCallback(): void {
+    super.connectedCallback();
+    this.addEventListener('keydown', this.onKeydown);
+  }
+
+  override disconnectedCallback(): void {
+    super.disconnectedCallback();
+    this.removeEventListener('keydown', this.onKeydown);
+  }
+
   override render() {
     return html`
       <form class="form" @submit="${this.onSubmit}">