fix(brand): unify calligraphy logo across header, footer and brand page

- logo.svg: remove dark-mode white fill so header/hero calligraphy stays
  visible on white backgrounds and matches footer logo-white.svg
- about/brand: replace sans-serif brand title with BrandCalligraphyName,
  reusing the same AoyagiReisho SVG paths as the footer logo without
  loading the 4.4MB font file
- add unit tests for BrandCalligraphyName and document decision in CONTEXT.md

src/components/ui/brand-calligraphy-name.test.tsx

@@ -0,0 +1,31 @@
+import { describe, it, expect } from '@jest/globals';
+import { render } from '@testing-library/react';
+import '@testing-library/jest-dom';
+import { BrandCalligraphyName } from './brand-calligraphy-name';
+
+describe('BrandCalligraphyName', () => {
+  it('renders the four calligraphy glyph paths from the logo asset', () => {
+    const { container } = render(<BrandCalligraphyName />);
+    const svg = container.querySelector('svg');
+    expect(svg).toBeInTheDocument();
+    expect(svg).toHaveAttribute('viewBox', '0 -40 200 48');
+    expect(svg!.querySelectorAll('path')).toHaveLength(4);
+    expect(svg!.querySelectorAll('path')[0]!.getAttribute('d')).toContain('M 378.00 62.00');
+    expect(svg!.querySelectorAll('path')[3]!.getAttribute('d')).toContain('M 799.00 85.00');
+  });
+
+  it('is exposed as an image with a brand label by default', () => {
+    const { container } = render(<BrandCalligraphyName />);
+    const svg = container.querySelector('svg');
+    expect(svg).toHaveAttribute('role', 'img');
+    expect(svg).toHaveAttribute('aria-label', '睿新致遠');
+  });
+
+  it('can be hidden from assistive technology when paired with sr-only text', () => {
+    const { container } = render(<BrandCalligraphyName ariaHidden />);
+    const svg = container.querySelector('svg');
+    expect(svg).toHaveAttribute('aria-hidden', 'true');
+    expect(svg).not.toHaveAttribute('role');
+    expect(svg).not.toHaveAttribute('aria-label');
+  });
+});