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) ✓

.gitea/workflows/prod.yml

@@ -0,0 +1,55 @@
+name: Deploy site (production)
+
+# Déploie le site vitrine (packages/site) sur Plesk via FTPS (lftp), à l'identique
+# de lidge_web / tracksniff-web. Ne se déclenche que sur un changement du site.
+on:
+  push:
+    branches:
+      - main
+    paths:
+      - 'packages/site/**'
+      - '.gitea/workflows/prod.yml'
+  workflow_dispatch:
+
+concurrency:
+  group: deploy-site
+  cancel-in-progress: true
+
+jobs:
+  build-and-deploy:
+    runs-on: ubuntu-latest
+    container:
+      image: node:22-bookworm
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+
+      # Install scopé au workspace du site : pas de build des deps natives du
+      # serveur (node-pty / node:sqlite) qui n'ont rien à faire ici.
+      - name: Install deps (@arboretum/site)
+        run: npm install -w @arboretum/site --no-audit --no-fund
+
+      - name: Build site
+        run: npm run build:site
+
+      - name: Check build output
+        run: ls -la packages/site/dist
+
+      - name: Deploy via FTPS (lftp)
+        run: |
+          if [ -z "$REMOTE_PATH" ]; then
+            echo "::error::Secret SITE_REMOTE_PATH manquant (chemin docroot du vhost git-arboretum.com)."
+            exit 1
+          fi
+          apt-get update && apt-get install -y lftp
+          lftp -c "
+          open -u \"$FTP_USER\",\"$FTP_PASSWORD\" \"$FTP_HOST\"
+          set ssl:verify-certificate no
+          mirror -R --delete --verbose packages/site/dist \"$REMOTE_PATH\"
+          "
+        env:
+          FTP_HOST: ${{ secrets.FTP_HOST }}
+          FTP_USER: ${{ secrets.FTP_USER }}
+          FTP_PASSWORD: ${{ secrets.FTP_PASSWORD }}
+          # Chemin docroot du vhost git-arboretum.com sur Plesk (ex. /httpdocs/arboretum/public).
+          REMOTE_PATH: ${{ secrets.SITE_REMOTE_PATH }}