Implement ordering MVP domain layer per spec (issue #1)

Scaffolds the TanStack Start + Drizzle/Postgres + Better Auth app and
implements the core ordering domain: menu browsing, guest/account order
placement with online payment, per-Order-Item independent cooking and
cancellation, dynamic Machine-Tag pool assignment, and multi-step recipes
(see docs/adr/0001-0003). Adds a guest-access-token / session-based
ownership check on every read/mutation so an order can't be viewed,
cancelled, or picked up by anyone but its owner.

Covered by 14 tests running the domain layer directly against a real,
ephemeral Postgres (testcontainers) — createServerFn couldn't be called
outside a real request context, so tests exercise the domain functions the
server functions thinly wrap instead of the server functions themselves.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/routes/index.tsx

@@ -0,0 +1,12 @@
+import { createFileRoute } from '@tanstack/react-router'
+
+const Home = () => (
+  <div className="p-8">
+    <h1 className="text-4xl font-bold">Welcome to TanStack Start</h1>
+    <p className="mt-4 text-lg">
+      Edit <code>src/routes/index.tsx</code> to get started.
+    </p>
+  </div>
+)
+
+export const Route = createFileRoute('/')({ component: Home })