refactor(custom-fields) : unify 3 parallel implementations into 1 module

Replace ~2900 lines across 9 files with ~400 lines in 2 files:
- shared/utils/customFields.ts (types + pure helpers)
- composables/useCustomFieldInputs.ts (reactive composable)

Migrated all consumers:
- Backend: add defaultValue to API Platform serialization groups
- Standalone pages: component edit/create, piece edit/create, product edit/create/detail
- Machine page: MachineCustomFieldsCard, MachineInfoCard, useMachineDetailCustomFields
- Hierarchy: ComponentItem, PieceItem
- Shared: CustomFieldDisplay, CustomFieldInputGrid
- Category editor: componentStructure.ts

Deleted:
- entityCustomFieldLogic.ts (335 lines)
- customFieldUtils.ts (440 lines)
- customFieldFormUtils.ts (404 lines)
- useEntityCustomFields.ts (181 lines)
- customFieldFormUtils.test.ts

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

frontend/app/composables/useComponentCreate.ts

@@ -17,15 +17,9 @@ import { useProductTypes } from '~/composables/useProductTypes'
 import { useApi } from '~/composables/useApi'
 import { useToast } from '~/composables/useToast'
 import { humanizeError } from '~/shared/utils/errorMessages'
-import { useCustomFields } from '~/composables/useCustomFields'
 import { useDocuments } from '~/composables/useDocuments'
 import { formatStructurePreview, normalizeStructureForEditor } from '~/shared/modelUtils'
-import {
-  type CustomFieldInput,
-  normalizeCustomFieldInputs,
-  requiredCustomFieldsFilled as _requiredCustomFieldsFilled,
-  saveCustomFieldValues as _saveCustomFieldValues,
-} from '~/shared/utils/customFieldFormUtils'
+import { useCustomFieldInputs, type CustomFieldInput } from '~/composables/useCustomFieldInputs'
 import { useConstructeurLinks } from '~/composables/useConstructeurLinks'
 import { uniqueConstructeurIds, constructeurIdsFromLinks } from '~/shared/constructeurUtils'
 import type { ConstructeurLinkEntry } from '~/shared/constructeurUtils'
@@ -77,7 +71,6 @@ export function useComponentCreate() {
     loading: productsLoading,
   } = useProducts()
   const toast = useToast()
-  const { upsertCustomFieldValue, updateCustomFieldValue } = useCustomFields()
   const { uploadDocuments } = useDocuments()
   const { syncLinks } = useConstructeurLinks()
   const { canEdit } = usePermissions()
@@ -98,7 +91,20 @@ export function useComponentCreate() {
   const constructeurLinks = ref<ConstructeurLinkEntry[]>([])
   const constructeurIdsFromForm = computed(() => constructeurIdsFromLinks(constructeurLinks.value))
   const lastSuggestedName = ref('')
-  const customFieldInputs = ref<CustomFieldInput[]>([])
+  const createdComponentId = ref<string | null>(null)
+
+  const {
+    fields: customFieldInputs,
+    requiredFilled: requiredCustomFieldsFilled,
+    saveAll: saveAllCustomFields,
+    refresh: refreshCustomFieldInputs,
+  } = useCustomFieldInputs({
+    definitions: computed(() => selectedTypeStructure.value?.customFields ?? []),
+    values: computed(() => []),
+    entityType: 'composant',
+    entityId: createdComponentId,
+  })
+
   const structureAssignments = ref<StructureAssignmentNode | null>(null)
   const selectedDocuments = ref<File[]>([])
   const uploadingDocuments = ref(false)
@@ -165,10 +171,6 @@ export function useComponentCreate() {
     return isAssignmentNodeComplete(structureAssignments.value, true)
   })
 
-  const requiredCustomFieldsFilled = computed(() =>
-    _requiredCustomFieldsFilled(customFieldInputs.value),
-  )
-
   const canSubmit = computed(() => Boolean(
     canEdit.value
     && selectedType.value
@@ -225,7 +227,6 @@ export function useComponentCreate() {
   watch(selectedType, (type) => {
     if (!type) {
       clearCreationForm()
-      customFieldInputs.value = []
       structureAssignments.value = null
       return
     }
@@ -233,7 +234,8 @@ export function useComponentCreate() {
       creationForm.name = type.name
     }
     lastSuggestedName.value = creationForm.name
-    customFieldInputs.value = normalizeCustomFieldInputs(selectedTypeStructure.value)
+    // useCustomFieldInputs auto-refreshes via its watcher on definitions
+    refreshCustomFieldInputs()
     structureAssignments.value = initializeStructureAssignments(selectedTypeStructure.value)
   })
 
@@ -323,12 +325,11 @@ export function useComponentCreate() {
       const result = await createComposant(payload)
       if (result.success) {
         const createdComponent = result.data as Record<string, any>
-        await _saveCustomFieldValues(
-          'composant',
-          createdComponent.id,
-          [createdComponent?.typeComposant?.structure?.customFields],
-          { customFieldInputs, upsertCustomFieldValue, updateCustomFieldValue, toast },
-        )
+        createdComponentId.value = createdComponent.id
+        const failedFields = await saveAllCustomFields()
+        if (failedFields.length) {
+          toast.showError(`Erreur sur les champs : ${failedFields.join(', ')}`)
+        }
         if (selectedDocuments.value.length && result.data?.id) {
           uploadingDocuments.value = true
           const uploadResult = await uploadDocuments(