feat: Add packages/site — landing vitrine (Vue 3 + Tailwind 4)

- Scaffold packages/site with 11 Vue components: hero (animated terminal), features, showcase, work groups, how-it-works, security, FAQ accordion, footer
- i18n EN/FR via vue-i18n with 82+ keys, autodetect navigator.language, toggle without reload
- Animated timeline (terminal, dialog, toast) ported from design, scroll-reveal, copy buttons (2 instances)
- Self-hosted JetBrains Mono fonts (@fontsource), optimized assets (mark 28KB, og-cover 1200×630)
- SEO: canonical, og:image, theme-color, robots.txt, sitemap.xml for git-arboretum.com
- Monorepo integration (decoupled from npm release): build:site / dev:site / preview:site scripts
- CI: add build:site step to ci.yml for early detection; create .gitea/workflows/prod.yml for FTPS deploy (lftp mirror) to git-arboretum.com
- Validated builds ✓ and UI rendering (EN/FR headless test) ✓

packages/site/src/composables/useScrollReveal.ts

@@ -0,0 +1,52 @@
+import type { Directive } from 'vue';
+
+// Directive `v-reveal` : révèle un bloc quand il entre dans le viewport.
+// Reprend l'intention du setupReveal() du design (seuil ~92% de la hauteur),
+// via un IntersectionObserver partagé. Respecte prefers-reduced-motion.
+let reducedMotion = false;
+try {
+  reducedMotion = window.matchMedia('(prefers-reduced-motion: reduce)').matches;
+} catch {
+  /* matchMedia indisponible */
+}
+
+let observer: IntersectionObserver | null = null;
+
+function getObserver(): IntersectionObserver | null {
+  if (typeof IntersectionObserver === 'undefined') return null;
+  if (!observer) {
+    observer = new IntersectionObserver(
+      (entries) => {
+        for (const entry of entries) {
+          if (entry.isIntersecting) {
+            entry.target.classList.add('is-visible');
+            observer?.unobserve(entry.target);
+          }
+        }
+      },
+      // -8% en bas ≈ déclenche quand le haut du bloc franchit ~92% du viewport.
+      { threshold: 0, rootMargin: '0px 0px -8% 0px' },
+    );
+  }
+  return observer;
+}
+
+export const reveal: Directive<HTMLElement> = {
+  mounted(el) {
+    el.classList.add('reveal');
+    if (reducedMotion) {
+      el.classList.add('is-visible');
+      return;
+    }
+    const io = getObserver();
+    if (!io) {
+      // Pas d'IntersectionObserver : on révèle immédiatement (pas de contenu caché).
+      el.classList.add('is-visible');
+      return;
+    }
+    io.observe(el);
+  },
+  unmounted(el) {
+    observer?.unobserve(el);
+  },
+};