feat(versioning) : add entity versioning frontend with restore flow

- useEntityVersions composable (list, preview, restore API calls)
- EntityVersionList component with auto-refresh after save
- VersionRestoreModal with context-aware messages per entity type
- Integrate into machine, composant, piece, product detail pages
- Add restore action label to historyDisplayUtils
- Show structure slots in composant/piece consultation mode

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

app/composables/useEntityVersions.ts

@@ -0,0 +1,98 @@
+import { ref, toValue } from 'vue'
+import { useApi } from '~/composables/useApi'
+import type { MaybeRef } from 'vue'
+
+export interface VersionEntry {
+  version: number
+  action: 'create' | 'update' | 'restore' | string
+  createdAt: string
+  actor: { id: string; label: string } | null
+  diff: Record<string, { from: unknown; to: unknown }> | null
+}
+
+export interface RestorePreview {
+  version: number
+  restoreMode: 'full' | 'partial'
+  diff: Record<string, { current: unknown; restored: unknown }>
+  warnings: Array<{
+    field: string
+    message: string
+    missingEntityId: string | null
+    missingEntityName: string | null
+  }>
+  snapshot: Record<string, unknown>
+}
+
+export interface RestoreResult {
+  success: boolean
+  newVersion: number
+  restoredFromVersion: number
+  restoreMode: 'full' | 'partial'
+  warnings: RestorePreview['warnings']
+}
+
+const ENTITY_ENDPOINTS: Record<string, string> = {
+  machine: '/machines',
+  composant: '/composants',
+  piece: '/pieces',
+  product: '/products',
+}
+
+interface Deps {
+  entityType: MaybeRef<string>
+  entityId: MaybeRef<string>
+}
+
+export function useEntityVersions(deps: Deps) {
+  const { get, post } = useApi()
+
+  const versions = ref<VersionEntry[]>([])
+  const loading = ref(false)
+  const error = ref<string | null>(null)
+
+  const getPath = () => {
+    const type = toValue(deps.entityType)
+    const id = toValue(deps.entityId)
+    const base = ENTITY_ENDPOINTS[type]
+    return `${base}/${id}`
+  }
+
+  const fetchVersions = async () => {
+    loading.value = true
+    error.value = null
+    try {
+      const result = await get(`${getPath()}/versions`)
+      if (!result.success) {
+        error.value = result.error ?? 'Impossible de charger les versions.'
+        versions.value = []
+        return
+      }
+      versions.value = result.data?.items ?? []
+    }
+    catch (err: any) {
+      error.value = err?.message ?? 'Erreur inconnue'
+      versions.value = []
+    }
+    finally {
+      loading.value = false
+    }
+  }
+
+  const fetchPreview = async (version: number): Promise<RestorePreview | null> => {
+    const result = await get<RestorePreview>(`${getPath()}/versions/${version}/preview`)
+    if (!result.success || !result.data) {
+      return null
+    }
+    return result.data
+  }
+
+  const restore = async (version: number): Promise<RestoreResult | null> => {
+    const result = await post<RestoreResult>(`${getPath()}/versions/${version}/restore`, {})
+    if (!result.success || !result.data) {
+      return null
+    }
+    return result.data
+  }
+
+  return { versions, loading, error, fetchVersions, fetchPreview, restore }
+}