fix(learning): load readme images over https

tests/unit/learning-project-image.test.tsx

@@ -0,0 +1,30 @@
+import { render, screen } from '@testing-library/react';
+import { describe, expect, it } from 'vitest';
+import { ProjectImage } from '@/pages/Learning/ProjectImage';
+
+describe('Learning ProjectImage', () => {
+  it('renders a credential-free HTTPS image only when direct loading is allowed', () => {
+    const { rerender } = render(
+      <ProjectImage
+        src="https://images.example.com/diagram.svg"
+        alt="项目结构图"
+        allowHttps
+      />,
+    );
+
+    expect(screen.getByAltText('项目结构图')).toHaveAttribute(
+      'src',
+      'https://images.example.com/diagram.svg',
+    );
+
+    rerender(
+      <ProjectImage
+        src="https://images.example.com/diagram.svg"
+        alt="项目结构图"
+      />,
+    );
+
+    expect(screen.queryByAltText('项目结构图')).not.toBeInTheDocument();
+    expect(screen.getByRole('img', { name: '项目结构图加载失败' })).toBeInTheDocument();
+  });
+});