feat : add Project DTO and service (frontend)

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

frontend/services/dto/project.ts

@@ -0,0 +1,17 @@
+import type { Client } from './client'
+
+export type Project = {
+    id: number
+    '@id'?: string
+    name: string
+    description: string | null
+    color: string
+    client: Client | null
+}
+
+export type ProjectWrite = {
+    name: string
+    description: string | null
+    color: string
+    client: string | null  // IRI : "/api/clients/1" ou null
+}