Add landing page with auth-aware routing and placeholder pages

Landing page greets unauthenticated visitors and redirects signed-in
users to /dashboard. Sign in and sign up buttons route to placeholder
pages. Dashboard page guards its route and redirects unauthenticated
users back to /.

Closes #42

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: dcl10

frontend/app/dashboard/page.tsx

@@ -0,0 +1,19 @@
+import { redirect } from "next/navigation";
+
+import { getSession } from "@/lib/auth";
+
+export default async function DashboardPage() {
+  const session = await getSession();
+  if (!session) redirect("/");
+
+  return (
+    <main className="flex flex-col items-center justify-center min-h-screen bg-paper px-6 text-center">
+      <h1 className="text-3xl font-bold tracking-[-0.025em] text-ink mb-3">
+        Your project dashboard
+      </h1>
+      <p className="text-[15px] text-ink-soft">
+        Dashboard functionality coming soon.
+      </p>
+    </main>
+  );
+}

frontend/app/page.tsx

@@ -1,31 +1,39 @@
-import { SignInButton, SignOutButton } from '@/lib/auth/components/auth-buttons'
-import { getSession } from '@/lib/auth'
+import Link from "next/link";
+import { redirect } from "next/navigation";
+
+import { LandingTopBar } from "@/components/shared";
+import { getSession } from "@/lib/auth";
 
 export default async function HomePage() {
-  const session = await getSession()
+  const session = await getSession();
+  if (session) redirect("/dashboard");
 
   return (
-    <main style={{ fontFamily: 'sans-serif', maxWidth: 640, margin: '4rem auto', padding: '0 1rem' }}>
-      <h1>SkillMatrixLlm</h1>
-
-      {session ? (
-        <>
-          <p>
-            Signed in as <strong>{session.user?.email ?? session.user?.name}</strong>
-          </p>
-          {session.error === 'RefreshAccessTokenError' && (
-            <p style={{ color: 'red' }}>
-              Your session has expired. Please sign in again.
-            </p>
-          )}
-          <SignOutButton />
-        </>
-      ) : (
-        <>
-          <p>You are not signed in.</p>
-          <SignInButton />
-        </>
-      )}
-    </main>
-  )
+    <>
+      <LandingTopBar />
+      <main className="flex flex-col items-center justify-center min-h-[calc(100vh-60px)] bg-paper px-6 text-center">
+        <h1 className="text-5xl font-bold tracking-[-0.03em] text-ink mb-4">
+          Welcome to Matchboard
+        </h1>
+        <p className="text-[17px] text-ink-soft max-w-[520px] mb-10">
+          The Digital Research Service skills-matching platform. Connect
+          researchers with the expertise your project needs.
+        </p>
+        <div className="flex items-center gap-3">
+          <Link
+            href="/sign-in"
+            className="inline-flex items-center gap-2 font-sans font-medium tracking-[-0.005em] rounded-sm px-[16px] py-[9px] text-[14px] bg-paper text-ink border border-[var(--border-strong)] hover:bg-portland-stone transition-colors duration-[120ms]"
+          >
+            Sign in
+          </Link>
+          <Link
+            href="/sign-up"
+            className="inline-flex items-center gap-2 font-sans font-medium tracking-[-0.005em] rounded-sm px-[16px] py-[9px] text-[14px] bg-nottingham-blue text-paper border border-nottingham-blue hover:bg-[var(--color-primary-deep)] transition-colors duration-[120ms]"
+          >
+            Sign up
+          </Link>
+        </div>
+      </main>
+    </>
+  );
 }

frontend/app/sign-in/page.tsx

@@ -0,0 +1,20 @@
+import Link from "next/link";
+
+export default function SignInPage() {
+  return (
+    <main className="flex flex-col items-center justify-center min-h-screen bg-paper px-6 text-center">
+      <h1 className="text-3xl font-bold tracking-[-0.025em] text-ink mb-3">
+        Sign in
+      </h1>
+      <p className="text-[15px] text-ink-soft mb-8">
+        Sign-in functionality coming soon.
+      </p>
+      <Link
+        href="/"
+        className="text-[14px] font-medium text-nottingham-blue hover:underline"
+      >
+        Back to home
+      </Link>
+    </main>
+  );
+}

frontend/app/sign-up/page.tsx

@@ -0,0 +1,20 @@
+import Link from "next/link";
+
+export default function SignUpPage() {
+  return (
+    <main className="flex flex-col items-center justify-center min-h-screen bg-paper px-6 text-center">
+      <h1 className="text-3xl font-bold tracking-[-0.025em] text-ink mb-3">
+        Sign up
+      </h1>
+      <p className="text-[15px] text-ink-soft mb-8">
+        Sign-up functionality coming soon.
+      </p>
+      <Link
+        href="/"
+        className="text-[14px] font-medium text-nottingham-blue hover:underline"
+      >
+        Back to home
+      </Link>
+    </main>
+  );
+}