feat(web): favicon (SVG) + apple-touch-icon (Next ImageResponse)

app/icon.svg — 32px vector with the brand 'M' (logo-matching) on #6366F1 indigo
rounded square. Sharp at every browser size.

app/apple-icon.tsx — 180x180 PNG rendered at request time via next/og
ImageResponse with the same design scaled up. Covers iOS home-screen + iPadOS.

Next 15 auto-discovers both via the file-based metadata convention and injects:
  <link rel='icon' href='/icon.svg' type='image/svg+xml' sizes='any'>
  <link rel='apple-touch-icon' href='/apple-icon' type='image/png' sizes='180x180'>

Verified: both URLs return 200, both link tags appear in the rendered HTML head,
brand matches the in-page Logo component.

apps/web/app/icon.svg

@@ -0,0 +1,4 @@
+<svg width="32" height="32" viewBox="0 0 32 32" xmlns="http://www.w3.org/2000/svg">
+  <rect width="32" height="32" rx="7" fill="#6366F1"/>
+  <path d="M8.5 22.5V9.5L16 16L23.5 9.5V22.5" stroke="#FFFFFF" stroke-width="2.4" stroke-linecap="round" stroke-linejoin="round" fill="none"/>
+</svg>