feat(www): landing page (#25)

* design: landing page spec + app icon asset

* chore(www): add anime.js, fonts, and landing page screenshot assets

* feat(www): add design tokens, fonts, shared layout

* feat(www): add landing page sections and styling

* feat(www): add theme toggle and anime.js viewport animations

* feat(www): feedback updates — no hero card, os-aware download, footer email, lowercase colored heading

* feat(www): remove screenshot borders, move macos hint below ctas, mobile github fallback

* feat(www): keep hero CTAs side by side

* feat(www): set initial nav border to transparent

* feat(www): add Rybbit prod-only, sitemap, SEO head, OG image, robots.txt, 404 page

* docs(AGENTS): include www landing page version in release sync checklist

* chore(www): add railpack.json for Dokploy deploy (force node provider, TZ)

* chore(www): use bun for Railpack deploy (packageManager + standalone www/bun.lock)

* docs(AGENTS): note www/bun.lock sync for Railpack deploys

* chore(www): add vitest test tooling

* feat(www): add FAQ data source

* feat(www): add SEO JSON-LD builders

* feat(www): add Seo JSON-LD component

* feat(www): wire Seo component and social/meta tags into Layout

* feat(www): add homepage JSON-LD, keyword H1, data-driven FAQ

* fix(www): point Roadmap footer link to GitHub

* feat(www): add lastmod to sitemap

* perf(www): self-host anime.js

* refactor(www): move nav and footer into shared Layout

* feat(www): add changelog page

* fix(www): make shared component styles global in Layout

* perf(www): optimize screenshots with Astro Image (webp/avif + srcset)

* feat(www): add web app manifest

* feat(www): add helpful links to 404 page

* fix(www): shorten homepage H1 copy

* fix(www): OS-aware navbar download + footer layout

* feat(www): build full changelog from v0.7.0 to v0.7.10

www/src/pages/404.astro

@@ -0,0 +1,20 @@
+---
+import Layout from "../layouts/Layout.astro";
+
+const title = "Page not found — Gridline";
+const description = "That page doesn’t exist. Head back to Gridline, the open-source database GUI.";
+---
+
+<Layout title={title} description={description} noIndex>
+  <main class="min-h-screen flex flex-col items-center justify-center px-6 text-center">
+    <p class="font-mono text-xs tracking-[0.15em] uppercase text-[var(--accent)] mb-4">404</p>
+    <h1 class="font-serif text-5xl md:text-7xl tracking-tight mb-4 lowercase">Lost in the schema.</h1>
+    <p class="text-[var(--text-muted)] max-w-md mb-8">
+      We couldn’t find that page. It may have been renamed, removed, or never existed.
+    </p>
+    <div class="flex flex-wrap items-center justify-center gap-3">
+      <a href="/" class="primary-btn">Back home</a>
+      <a href="/changelog" class="ghost-btn">Changelog</a>
+    </div>
+  </main>
+</Layout>