feat(website): add the project site and deploy it to GitHub Pages

A Vite + React + TypeScript + Tailwind v4 site under website/, built from
the soulseek-rs design system so the site and the TUI stay one product.
The colour tokens in src/index.css are the same values as
soulseek-rs/src/ui/styles.rs; change one, change both.

The hero is a working recreation of the TUI: it plays one scripted run and
then takes the keyboard, or lands on the resting state directly under
prefers-reduced-motion. Its sample data is invented or public domain, per
the tone-of-voice guardrail against naming copyrighted material.

Static output rather than an SPA shell. `bun run build` compiles the client,
compiles the same app for Node, then renders every route in src/lib/routes.ts
to its own file with that route's title, description and canonical URL. A
direct link to /install therefore answers 200 with real markup instead of
GitHub's 404 page. routes.ts is keyed into App.tsx by literal path, so adding
one without the other fails typecheck rather than shipping a page whose body
says "not found" under the right title.

Theme is resolved once by an inline script before first paint and adopted by
React through useSyncExternalStore, so there is no flash and no hydration
mismatch on the toggle. Light mode re-cuts the semantic hues darker: phosphor
and tape read on vinyl but wash out on manila.

CI and release skip website-only pushes, and Pages skips Rust-only ones. The
two Rust workflows share one paths-ignore list so they can only skip
together, which keeps the release ci-gate from polling for a run that was
never queued. That gate also now treats a cancelled CI as "keep waiting"
rather than a failure, since cancel-in-progress cancels the older SHA on
every back-to-back push.

website/src/pages/not-found.tsx

@@ -0,0 +1,34 @@
+import { Button } from '@/components/ui/button'
+import { Eyebrow, Wrap } from '@/components/ui/layout'
+import { Terminal } from '@/components/ui/terminal'
+
+export const NotFound = () => {
+  return (
+    <section className="py-16">
+      <Wrap>
+        <div className="flex max-w-[560px] flex-col gap-3.5">
+          <Eyebrow>404</Eyebrow>
+          <h1 className="text-[26px] leading-[34px] font-medium sm:text-title sm:leading-[var(--text-title--line-height)]">
+            No such path.
+          </h1>
+          <p className="text-secondary">
+            That page doesn&rsquo;t exist. The four that do are in the nav above.
+          </p>
+          <Terminal
+            lines={[
+              { t: 'cmd', text: 'soulseek-rs --help' },
+              { t: 'cm', text: '# no such page: check the nav, or start here' },
+            ]}
+            copy="soulseek-rs --help"
+          />
+          <div className="mt-1.5 flex flex-wrap gap-2 sm:gap-3">
+            <Button href="/" variant="accent">
+              Home
+            </Button>
+            <Button href="/docs">Read the docs</Button>
+          </div>
+        </div>
+      </Wrap>
+    </section>
+  )
+}