fix(web): make the favicon follow the color scheme

favicon.svg embeds @media (prefers-color-scheme: dark) so the DeepSeek
mark turns white under a dark browser scheme; index.html and the install
manifest gain a 32x32 PNG fallback (brand blue) for Safari, which cannot
render SVG favicons. pwa-manifest.e2e.ts pins the PNG link, both manifest
icons, and the dark media query.

apps/web/tests/pwa-manifest.e2e.ts

@@ -8,6 +8,7 @@ const DIST_ROOT = fileURLToPath(new URL('../dist', import.meta.url))
 it('ships install metadata with the built web application', async () => {
   const index = await readFile(join(DIST_ROOT, 'index.html'), 'utf8')
   expect(index).toContain('<link rel="manifest" href="/manifest.webmanifest" />')
+  expect(index).toContain('<link rel="icon" type="image/png" sizes="32x32" href="/favicon-32x32.png" />')
 
   const manifest: unknown = JSON.parse(await readFile(join(DIST_ROOT, 'manifest.webmanifest'), 'utf8'))
   expect(manifest).toEqual({
@@ -17,11 +18,25 @@ it('ships install metadata with the built web application', async () => {
     start_url: '/',
     scope: '/',
     display: 'fullscreen',
-    icons: [{
-      src: '/favicon.svg',
-      sizes: 'any',
-      type: 'image/svg+xml',
-      purpose: 'any',
-    }],
+    icons: [
+      {
+        src: '/favicon-32x32.png',
+        sizes: '32x32',
+        type: 'image/png',
+        purpose: 'any',
+      },
+      {
+        src: '/favicon.svg',
+        sizes: 'any',
+        type: 'image/svg+xml',
+        purpose: 'any',
+      },
+    ],
   })
 })
+
+it('ships a favicon that switches to a light mark under dark color scheme', async () => {
+  const favicon = await readFile(join(DIST_ROOT, 'favicon.svg'), 'utf8')
+  expect(favicon).toContain('@media (prefers-color-scheme: dark)')
+  expect(favicon).toMatch(/path\s*{[^}]*fill:\s*#fff/i)
+})