feat(system): page Status avec endpoint API Platform et composants Vue

- Nouveau domaine System/Domain/Model/SystemStatus (value object)
- QueryHandler agrégeant métriques mangas, chapitres, jobs (global/24h/7j), stockage et sources
- Endpoint GET /api/system/status via API Platform (singleton)
- Calcul de l'espace disque par RecursiveDirectoryIterator sur public/images
- Page Vue /system/status avec 6 cards (Mangas, Chapitres, Jobs, Stockage, Sources, Système)
- Nettoyage du router : suppression des PlaceholderComponent et routes placeholder
- Sidebar : suppression des entrées sans page réelle

assets/vue/app/domain/system/presentation/pages/StatusPage.vue

@@ -0,0 +1,71 @@
+<template>
+    <div class="flex flex-col h-full">
+        <Toolbar :config="toolbarConfig" />
+
+        <div class="overflow-y-auto flex-1">
+            <!-- Loading -->
+            <div v-if="loading" class="flex justify-center py-12">
+                <div class="animate-spin h-10 w-10 border-b-2 border-blue-500 rounded-full"></div>
+            </div>
+
+            <!-- Error -->
+            <div v-else-if="error" class="px-6 py-8">
+                <div class="bg-red-50 dark:bg-red-900 border border-red-200 dark:border-red-700 p-4 rounded">
+                    <div class="flex items-center">
+                        <ExclamationCircleIcon class="w-5 h-5 text-red-400 mr-2 shrink-0" />
+                        <p class="text-red-800 dark:text-red-200">{{ error }}</p>
+                    </div>
+                    <button
+                        @click="statusStore.loadStatus()"
+                        class="mt-3 px-4 py-2 bg-red-600 text-white hover:bg-red-700 rounded">
+                        Réessayer
+                    </button>
+                </div>
+            </div>
+
+            <!-- Données -->
+            <div v-else-if="status" class="grid grid-cols-1 md:grid-cols-2 xl:grid-cols-3 gap-4 p-4">
+                <MangasStatusCard :status="status" />
+                <ChaptersStatusCard :status="status" />
+                <JobsStatusCard :status="status" />
+                <StorageStatusCard :status="status" />
+                <SourcesStatusCard :status="status" />
+                <SystemInfoCard :status="status" />
+            </div>
+        </div>
+    </div>
+</template>
+
+<script setup>
+import { ArrowPathIcon, ExclamationCircleIcon } from '@heroicons/vue/24/outline';
+import { storeToRefs } from 'pinia';
+import { computed, onMounted } from 'vue';
+import Toolbar from '../../../../shared/components/ui/Toolbar.vue';
+import { useStatusStore } from '../../application/store/statusStore';
+import ChaptersStatusCard from '../components/ChaptersStatusCard.vue';
+import JobsStatusCard from '../components/JobsStatusCard.vue';
+import MangasStatusCard from '../components/MangasStatusCard.vue';
+import SourcesStatusCard from '../components/SourcesStatusCard.vue';
+import StorageStatusCard from '../components/StorageStatusCard.vue';
+import SystemInfoCard from '../components/SystemInfoCard.vue';
+
+const statusStore = useStatusStore();
+const { status, loading, error } = storeToRefs(statusStore);
+
+onMounted(() => statusStore.loadStatus());
+
+const toolbarConfig = computed(() => ({
+    leftSection: [
+        { type: 'label', text: 'Statut système', class: 'text-sm font-medium' },
+    ],
+    rightSection: [
+        {
+            type: 'button',
+            icon: ArrowPathIcon,
+            label: 'Rafraîchir',
+            disabled: loading.value,
+            onClick: () => statusStore.loadStatus(),
+        },
+    ],
+}));
+</script>