feat: public marketing site (vitrine)

Adds a (marketing) route group -- Home, Features, About, Privacy,
Terms, Contact -- reusing the app's design system/i18n/deploy
pipeline rather than a separate site. Root page.tsx now branches on
session instead of always redirecting to /recipes: logged-in visitors
still land in the app unchanged, logged-out visitors see the vitrine
home page.

The actual integration point: proxy.ts's PUBLIC_PATHS previously sent
every anonymous "/" request straight to /login before page.tsx's
redirect ever ran. Added the new marketing routes to PUBLIC_PATHS,
plus a separate exact-match list for "/" itself -- it can't go in the
startsWith-matched array, since every path starts with "/" and that
would make the whole app public.

Also adds app/sitemap.ts and app/robots.ts (neither existed before),
disallowing the authenticated app and the unlisted /r/ and /s/ share
routes from crawling while allowing /u/ public profiles.

Pricing page deliberately not included -- waiting on Stripe Checkout
(STRIPE_PLAN.md) so its CTA goes somewhere real. Privacy/Terms are
structural drafts flagged inline as not lawyer-reviewed, per
STRIPE_PLAN.md's own tax-advice caveat -- same spirit here.

Verified with a full production build (pnpm build) -- compiles clean,
all 7 new routes render, since there's no DB in this sandbox to run
the dev server against for a real click-through.

v0.48.0

apps/web/app/(marketing)/contact/page.tsx

@@ -0,0 +1,29 @@
+import type { Metadata } from "next";
+import { Mail } from "lucide-react";
+import { getMessages } from "@/lib/i18n/server";
+
+export const metadata: Metadata = {
+  title: "Contact — Epicure",
+  description: "Get in touch with the Epicure team.",
+};
+
+const SUPPORT_EMAIL = "support@epicure.app";
+
+export default function ContactPage() {
+  const m = getMessages(undefined);
+  const t = m.marketing.contact;
+
+  return (
+    <div className="container mx-auto px-4 py-16 max-w-lg text-center space-y-6">
+      <h1 className="text-3xl font-bold tracking-tight">{t.title}</h1>
+      <p className="text-muted-foreground">{t.subtitle}</p>
+      <a
+        href={`mailto:${SUPPORT_EMAIL}`}
+        className="inline-flex items-center gap-2 rounded-lg border px-4 py-2.5 text-sm font-medium hover:bg-accent transition-colors"
+      >
+        <Mail className="h-4 w-4" />
+        {SUPPORT_EMAIL}
+      </a>
+    </div>
+  );
+}