feat: implement auth, projects, and frontend foundation

apps/web/src/pages/placeholder.tsx

@@ -0,0 +1,32 @@
+export const PlaceholderPage = ({ title }: { title: string }) => {
+  return (
+    <section className="stack">
+      <h1>{title}</h1>
+      <p className="muted">This page is part of the frontend foundation scaffold.</p>
+    </section>
+  );
+};
+
+export const NotFoundPage = () => {
+  return (
+    <section className="stack center-screen">
+      <h1>404</h1>
+      <p className="muted">The page you requested does not exist.</p>
+    </section>
+  );
+};
+
+export const LoginRedirectPage = () => {
+  const nextPath = new URLSearchParams(window.location.search).get("next") ?? "/";
+  const encodedNext = encodeURIComponent(nextPath);
+
+  return (
+    <section className="stack center-screen">
+      <h1>Sign in required</h1>
+      <p className="muted">You need to authenticate to access this section.</p>
+      <a className="primary-button" href={`/auth/login?next=${encodedNext}`}>
+        Continue to login
+      </a>
+    </section>
+  );
+};