feat: scaffold Astro project with layout, nav, hero and concept sections

- Add global ocean-themed styles (Inter + Sora, glassmorphism utilities).
- Wire up base layout, sticky nav and footer respecting base path.
- Build hero with stylised rock SVG + sonar ambient rings and concept pipeline schematic.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/components/Footer.astro

@@ -0,0 +1,30 @@
+---
+const year = new Date().getFullYear();
+---
+
+<footer class="relative border-t border-white/5 py-12 mt-12">
+  <div class="container-narrow flex flex-col gap-6 md:flex-row md:items-center md:justify-between">
+    <div class="flex items-center gap-3">
+      <span class="inline-flex h-8 w-8 items-center justify-center rounded-md bg-gradient-to-br from-tide-500 to-lagoon-500">
+        <svg viewBox="0 0 24 24" class="h-5 w-5 text-abyss-950" fill="currentColor" aria-hidden="true">
+          <path d="M2 16c2 0 2-2 4-2s2 2 4 2 2-2 4-2 2 2 4 2 2-2 4-2v4H2z"/>
+          <circle cx="12" cy="9" r="2"/>
+        </svg>
+      </span>
+      <div>
+        <div class="font-display font-semibold">NowYouSea</div>
+        <div class="text-xs text-foam-100/60">Le rocher connecté qui écoute l'océan.</div>
+      </div>
+    </div>
+
+    <nav aria-label="Navigation pied de page" class="flex flex-wrap gap-x-6 gap-y-2 text-sm text-foam-100/60">
+      <a href="#concept" class="hover:text-tide-400">Concept</a>
+      <a href="#configurations" class="hover:text-tide-400">Configurations</a>
+      <a href="#architecture" class="hover:text-tide-400">Architecture</a>
+      <a href="#equipe" class="hover:text-tide-400">Équipe</a>
+      <a href="#contact" class="hover:text-tide-400">Contact</a>
+    </nav>
+
+    <div class="text-xs text-foam-100/50">© {year} NowYouSea — Tous droits réservés.</div>
+  </div>
+</footer>