Refactor : renommage ClientBrief en Brief (plus générique)

- Brief.vue masque les boutons d'ajout pour extended-brief
- Éditable uniquement en back-office pour cette étape
- ClientBrief → Brief dans ProjectStep.vue

Ref #3

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

src/components/project/ProjectStep.vue

@@ -23,7 +23,7 @@ import 'dayjs/locale/fr';
 import { usePageStore } from '../../stores/page';
 import { computed, onMounted, useTemplateRef } from 'vue';
 import { useProjectStore } from '../../stores/project';
-import ClientBrief from './cards/ClientBrief.vue';
+import Brief from './cards/Brief.vue';
 import MultipleDocuments from './cards/MultipleDocuments.vue';
 import SimpleDocument from './cards/SimpleDocument.vue';
 import VirtualSample from './cards/VirtualSample.vue';
@@ -35,9 +35,9 @@ const { step } = defineProps({
 });
 
 const cardsMap = {
-  clientBrief: ClientBrief,
+  clientBrief: Brief,
   proposal: MultipleDocuments,
-  extendedBrief: ClientBrief,
+  extendedBrief: Brief,
   industrialIdeation: SimpleDocument,
   virtualSample: VirtualSample,
   physicalSample: PhysicalSample,