feat(landing): migrate from Next.js to Astro 5

Zero client JS, 165 static pages, self-hosted fonts, Otter Orange
design system. Includes tool SEO data for all 157 tools, enterprise
page, and updated e2e landing tests.

apps/landing/src/pages/404.astro

@@ -0,0 +1,37 @@
+---
+import Footer from "@/components/Footer.astro";
+import Navbar from "@/components/Navbar.astro";
+import Base from "@/layouts/Base.astro";
+---
+
+<Base
+  title="Page Not Found | SnapOtter"
+  description="The page you are looking for does not exist."
+  noindex={true}
+>
+  <Navbar />
+
+  <main id="main" class="flex min-h-[60vh] flex-col items-center justify-center px-6 pt-32 pb-20 text-center">
+    <div class="reveal">
+      <p class="text-6xl font-bold text-primary">404</p>
+      <h1 class="mt-4 font-display text-3xl font-bold tracking-tight md:text-4xl">
+        Page not found
+      </h1>
+      <p class="mt-4 text-lg text-muted">
+        The page you are looking for does not exist or has been moved.
+      </p>
+      <a
+        href="/"
+        class="btn-primary mt-8 inline-flex items-center gap-2 rounded-lg px-6 py-3 text-sm font-semibold"
+      >
+        <svg class="h-4 w-4" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round">
+          <path d="m12 19-7-7 7-7" />
+          <path d="M19 12H5" />
+        </svg>
+        Back to homepage
+      </a>
+    </div>
+  </main>
+
+  <Footer />
+</Base>