refactor(api): extract shared extractCollection helper (F2.1)

Create shared/utils/apiHelpers.ts with generic extractCollection<T>()
that handles hydra:member, member, items, data, and array formats.
Replace 7 local implementations in CRUD composables.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app/composables/useDocuments.ts

@@ -2,6 +2,7 @@ import { ref } from 'vue'
 import { useApi } from './useApi'
 import { useToast } from './useToast'
 import { normalizeRelationIds } from '~/shared/apiRelations'
+import { extractCollection } from '~/shared/utils/apiHelpers'
 
 export interface Document {
   id: string
@@ -34,23 +35,6 @@ export interface DocumentResult {
 const documents = ref<Document[]>([])
 const loading = ref(false)
 
-const extractCollection = (payload: unknown): Document[] => {
-  if (Array.isArray(payload)) {
-    return payload
-  }
-  const p = payload as Record<string, unknown> | null
-  if (Array.isArray(p?.member)) {
-    return p.member as Document[]
-  }
-  if (Array.isArray(p?.['hydra:member'])) {
-    return p['hydra:member'] as Document[]
-  }
-  if (Array.isArray(p?.data)) {
-    return p.data as Document[]
-  }
-  return []
-}
-
 const fileToBase64 = (file: File): Promise<string> =>
   new Promise((resolve, reject) => {
     const reader = new FileReader()