feat(site,docs): aligne le site vitrine et la doc sur l'app « Emerald »

Site (packages/site) : adopte le design system Emerald (polices Inter +
JetBrains Mono variables, tokens sémantiques, thème clair/sombre + bascule)
et met les mockups à jour sur l'app réelle.

- style.css : tokens Emerald (@theme sombre + override html[data-theme=light]) ;
  lib/theme.ts + ThemeToggle.vue + anti-FOUC index.html ; sweep des couleurs
  brutes vers les tokens dans toutes les sections.
- Mockups fidèles à l'IDE multi-projet : HeroMockup (rail ActivityBar au lieu
  de la sidebar large + v obsolète retirée), ShowcaseSection (supervision au
  lieu du dashboard worktree-first, onglets mobiles réels), WorkspaceShowcase
  (diff-add/del, bouton commit accent-solid) ; framing « worktree-first »
  résiduel levé (i18n).
- og-cover.png rafraîchi (carte Emerald).

Docs : README.md + README.fr.md (retrait « Status: MVP », ajout du langage
Emerald + thème clair/sombre/système, VSIX 0.2.0 -> 0.3.0, section Screenshots),
vscode README (VSIX 0.3.0), brand README (thème clair), CHANGELOG daemon 3.2.0.
Captures IDE sombre + clair (brand/screenshot-ide-*.png).

packages/site/src/components/AppFooter.vue

@@ -9,7 +9,7 @@ const { t } = useI18n();
 </script>
 
 <template>
-  <footer class="relative z-[1] border-t border-[#1c1c1f]">
+  <footer class="relative z-[1] border-t border-border-soft">
     <div class="mx-auto flex max-w-[1200px] flex-wrap items-center justify-between gap-5 px-6 py-[34px]">
       <div class="flex items-center gap-[11px]">
         <img
@@ -20,28 +20,28 @@ const { t } = useI18n();
           class="h-[22px] w-[22px] object-contain"
           style="filter: grayscale(1) brightness(1.5); opacity: 0.4"
         />
-        <span class="font-mono text-sm text-zinc-300">git-arboretum.com</span>
-        <span class="ml-1 text-[13px] text-zinc-600">· {{ t('footTag') }}</span>
+        <span class="font-mono text-sm text-fg-muted">git-arboretum.com</span>
+        <span class="ml-1 text-[13px] text-fg-subtle">· {{ t('footTag') }}</span>
       </div>
       <div class="flex items-center gap-[22px] text-sm">
-        <a :href="REPO" target="_blank" rel="noopener" class="inline-flex items-center gap-1.5 text-zinc-400 no-underline transition-colors hover:text-emerald-400">
+        <a :href="REPO" target="_blank" rel="noopener" class="inline-flex items-center gap-1.5 text-fg-muted no-underline transition-colors hover:text-accent">
           <IconGitea :size="15" />
           Gitea
         </a>
-        <a :href="LICENSE" target="_blank" rel="noopener" class="text-zinc-400 no-underline transition-colors hover:text-emerald-400">
+        <a :href="LICENSE" target="_blank" rel="noopener" class="text-fg-muted no-underline transition-colors hover:text-accent">
           {{ t('license') }}
         </a>
         <a
           :href="COFFEE"
           target="_blank"
           rel="noopener"
-          class="inline-flex items-center gap-1.5 text-zinc-400 no-underline transition-colors hover:text-amber-400 focus-visible:rounded-md focus-visible:outline-2 focus-visible:outline-offset-2 focus-visible:outline-amber-400/70"
+          class="inline-flex items-center gap-1.5 text-fg-muted no-underline transition-colors hover:text-warn focus-visible:rounded-md focus-visible:outline-2 focus-visible:outline-offset-2 focus-visible:outline-warn/70"
         >
           <svg width="15" height="15" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="1.7" stroke-linecap="round" stroke-linejoin="round" aria-hidden="true"><path d="M10 2v2" /><path d="M14 2v2" /><path d="M5 8h13a1 1 0 0 1 1 1v2a4 4 0 0 1-4 4H8a4 4 0 0 1-4-4V9a1 1 0 0 1 1-1Z" /><path d="M6 15a4 4 0 0 0 4 4h2a4 4 0 0 0 4-4" /><path d="M19 9h1.5a2.5 2.5 0 0 1 0 5H18" /></svg>
           {{ t('coffee') }}
         </a>
         <div class="flex items-center gap-2">
-          <code class="font-mono text-[12.5px] text-zinc-600">{{ INSTALL_COMMAND }}</code>
+          <code class="font-mono text-[12.5px] text-fg-subtle">{{ INSTALL_COMMAND }}</code>
           <CopyButton variant="icon" :text="INSTALL_COMMAND" :label="t('copyCommand')" />
         </div>
       </div>