feat(docs-site): brand the docs to match the punktfunk website

Theme the Fumadocs docs site with the punktfunk identity, mirroring the
marketing site:

- Swap the stock `neutral` preset for `purple`, then override --color-fd-*
  with the violet lens-mark palette (#6c5bf3 / #a79ff8). The brand is the
  violet, not the site's blue marketing background, so the blue is not used
  as a reading surface; dark mode tints the chrome toward the app-icon
  violet-dark (#1c1530).
- Adopt @unom/ui's token contract (--brand/--primary/--accent + bg-brand
  etc.) as the shared token source, and @source its dist.
- Load Geist (the brand typeface) via @fontsource-variable/geist.
- Add the BrandMark lens to the nav + landing hero, wire the brand
  favicon.svg, and add Docs/Website nav links.
- Keep the Fumadocs light/dark toggle.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

docs-site/src/components/BrandMark.tsx

@@ -0,0 +1,29 @@
+// punktfunk brand mark: two overlapping circles forming a lens — the violet
+// brand identity. Copied verbatim from the marketing site (flattened from the
+// clients/apple punktfunk_Logo.icon). Back-to-front: large light-violet circle,
+// deep-violet circle, light highlight where they overlap.
+export default function BrandMark({ className }: { className?: string }) {
+  return (
+    <svg
+      aria-label="punktfunk"
+      role="img"
+      xmlns="http://www.w3.org/2000/svg"
+      viewBox="0 0 1000 1000"
+      className={className}
+    >
+      <title>punktfunk</title>
+      <path
+        d="M403.037,791.672c107.586,0 194.41,-86.824 194.41,-194.41c0,-107.586 -86.824,-194.41 -194.41,-194.41c-107.586,0 -194.41,86.824 -194.41,194.41c0,107.586 86.824,194.41 194.41,194.41Z"
+        fill="#a79ff8"
+      />
+      <path
+        d="M735.276,540.321c76.075,-76.075 76.075,-198.862 0,-274.937c-76.075,-76.075 -198.862,-76.075 -274.937,0c-76.075,76.075 -76.075,198.862 0,274.937c76.075,76.075 198.862,76.075 274.937,0Z"
+        fill="#6c5bf3"
+      />
+      <path
+        d="M647.84,590.737c-64.853,17.403 -136.871,0.597 -187.885,-50.416c-51.013,-51.013 -67.819,-123.032 -50.416,-187.885c64.853,-17.403 136.871,-0.597 187.885,50.416c51.013,51.013 67.819,123.032 50.416,187.885Z"
+        fill="#d2c9fb"
+      />
+    </svg>
+  )
+}