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/components/icons/IconGitea.vue

@@ -0,0 +1,22 @@
+<script setup lang="ts">
+withDefaults(defineProps<{ size?: number }>(), { size: 16 });
+</script>
+
+<template>
+  <svg
+    :width="size"
+    :height="size"
+    viewBox="0 0 24 24"
+    fill="none"
+    stroke="currentColor"
+    stroke-width="1.7"
+    stroke-linecap="round"
+    stroke-linejoin="round"
+    aria-hidden="true"
+  >
+    <path d="M4 10h12v4a4 4 0 0 1-4 4H8a4 4 0 0 1-4-4z" />
+    <path d="M16 11h2.5a2.5 2.5 0 0 1 0 5H16" />
+    <path d="M7 3c-.5.8.5 1.6 0 2.5" />
+    <path d="M11 3c-.5.8.5 1.6 0 2.5" />
+  </svg>
+</template>