feat(chat): add in-page overlay

extension/chat-format.test.mjs

@@ -0,0 +1,22 @@
+import { beforeAll, describe, expect, it } from 'vitest';
+
+beforeAll(async () => {
+    await import('./chat-format.js');
+});
+
+describe('chat formatting', () => {
+    it('escapes executable HTML before applying limited Markdown', () => {
+        const result = globalThis.KoalaSyncChatFormat.formatChatText('<img src=x onerror=alert(1)> **bold** *italic*');
+        expect(result).toBe('&lt;img src=x onerror=alert(1)&gt; <strong>bold</strong> <em>italic</em>');
+        expect(result).not.toContain('<img');
+    });
+
+    it('tokenizes only text, strong, and emphasis nodes', () => {
+        expect(globalThis.KoalaSyncChatFormat.tokenizeChatText('<script>x</script> **bold** *italic*')).toEqual([
+            { type: 'text', text: '<script>x</script> ' },
+            { type: 'strong', text: 'bold' },
+            { type: 'text', text: ' ' },
+            { type: 'em', text: 'italic' }
+        ]);
+    });
+});