feat(tui): add markdown rendering utility

src/frontends/tui/markdown.test.ts

@@ -0,0 +1,31 @@
+import { describe, it, expect } from 'vitest';
+import { renderMarkdown } from './markdown.js';
+
+describe('renderMarkdown', () => {
+  it('renders plain text unchanged', () => {
+    const result = renderMarkdown('Hello world');
+    expect(result).toContain('Hello world');
+  });
+
+  it('renders bold text', () => {
+    const result = renderMarkdown('This is **bold** text');
+    expect(result).toContain('bold');
+  });
+
+  it('renders code blocks', () => {
+    const result = renderMarkdown('```javascript\nconst x = 1;\n```');
+    expect(result).toContain('const');
+    expect(result).toContain('x');
+  });
+
+  it('renders inline code', () => {
+    const result = renderMarkdown('Use `console.log()` for debugging');
+    expect(result).toContain('console.log()');
+  });
+
+  it('renders lists', () => {
+    const result = renderMarkdown('- Item 1\n- Item 2');
+    expect(result).toContain('Item 1');
+    expect(result).toContain('Item 2');
+  });
+});