feat : init Central project — Symfony 8 + Nuxt 4 + Docker starter

Same architecture as Lesstime: API Platform 4, JWT auth, @malio/layer-ui,
PostgreSQL 16, Docker Compose (ports 8083/3003/5436), dark mode theme.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/pages/index.vue

@@ -0,0 +1,12 @@
+<template>
+    <div>
+        <h1 class="text-2xl font-bold text-neutral-900">Tableau de bord</h1>
+        <p class="mt-4 text-neutral-600">Bienvenue sur Central.</p>
+    </div>
+</template>
+
+<script setup lang="ts">
+useHead({
+    title: 'Tableau de bord'
+})
+</script>