feat(intake): post-submit thanks page

Phase 8a Task 12. Static page; no card read, no brief shown, no
link to the signed-in board. Resolves the token only to confirm it
is still alive — a revoked token landing here still shows 'Thanks'
so the submission cannot be probed.

src/app/intake/[token]/sent/[cardId]/page.tsx

@@ -0,0 +1,61 @@
+import Link from "next/link";
+
+import { resolveIntakeLink } from "@/lib/intake-links";
+
+/**
+ * The "thanks" page after a public submission.
+ *
+ * Intentionally static: it does not read the card, does not show the brief,
+ * does not link to the board. An anonymous submitter should see a clear
+ * acknowledgement and a way to file another request; nothing more. The card
+ * detail page is signed-in only, and linking to it from here would either
+ * 404 or force a session we deliberately do not require.
+ */
+export default async function IntakeSentPage({
+  params,
+}: {
+  params: Promise<{ token: string; cardId: string }>;
+}) {
+  const { token } = await params;
+
+  // We don't actually need the card or the link to render this page; we
+  // resolve the link only to confirm the token is still alive. A revoked
+  // token landing on /sent/ would otherwise confirm the submission
+  // happened — same "doesn't shout" property as the intake page.
+  const link = await resolveIntakeLink(token);
+  if (!link || !link.active) {
+    return (
+      <main className="mx-auto max-w-xl space-y-3 p-6">
+        <h1 className="text-lg font-semibold text-text-primary">Thanks</h1>
+        <p className="text-sm text-text-secondary">
+          Your message was sent.
+        </p>
+      </main>
+    );
+  }
+
+  return (
+    <main className="mx-auto max-w-xl space-y-4 p-6">
+      <header className="space-y-1">
+        <h1 className="text-lg font-semibold text-text-primary">Thanks</h1>
+        <p className="text-sm text-text-secondary">
+          Your request has been sent to the developer.
+        </p>
+      </header>
+
+      <p className="text-sm text-text-muted">
+        They will see it on their board and get back to you about what
+        happens next. There is no notification for you to wait on here.
+      </p>
+
+      <div className="border-t border-border-subtle pt-3">
+        <Link
+          href={`/intake/${token}`}
+          className="inline-flex items-center gap-1.5 rounded-lg border border-border-subtle px-3 py-1.5 text-sm text-text-secondary hover:bg-surface-raised"
+        >
+          Send another request
+        </Link>
+      </div>
+    </main>
+  );
+}