feat(directory) : add Clients/Prospects repertoire front layer

LST-58 (2.4) front. Completes the Directory module.

- New frontend/modules/directory/ layer (auto-detected): /directory page with
  Clients and Prospects tabs.
- Client front moved into the layer (clients service + client DTO +
  ClientDrawer). New prospects service, prospect DTO and ProspectDrawer (with
  a "Convert to client" action calling POST /prospects/{id}/convert).
- Consumers repointed to ~/modules/directory/... (admin client tab, PM project
  drawer + project pages + project DTO, time-tracking page + export drawer).
- Sidebar admin item /directory gated by the directory module; /directory
  protected by the admin middleware. i18n keys added (directory.*, prospects.*).

nuxt build passes; routes preserved.

Adds the 2.4 plan doc.

frontend/modules/directory/services/clients.ts

@@ -0,0 +1,32 @@
+import type { Client, ClientWrite } from './dto/client'
+import type { HydraCollection } from '~/utils/api'
+import { extractHydraMembers } from '~/utils/api'
+
+export function useClientService() {
+    const api = useApi()
+
+    async function getAll(): Promise<Client[]> {
+        const data = await api.get<HydraCollection<Client>>('/clients')
+        return extractHydraMembers(data)
+    }
+
+    async function create(payload: ClientWrite): Promise<Client> {
+        return api.post<Client>('/clients', payload as Record<string, unknown>, {
+            toastSuccessKey: 'clients.created',
+        })
+    }
+
+    async function update(id: number, payload: Partial<ClientWrite>): Promise<Client> {
+        return api.patch<Client>(`/clients/${id}`, payload as Record<string, unknown>, {
+            toastSuccessKey: 'clients.updated',
+        })
+    }
+
+    async function remove(id: number): Promise<void> {
+        await api.delete(`/clients/${id}`, {}, {
+            toastSuccessKey: 'clients.deleted',
+        })
+    }
+
+    return { getAll, create, update, remove }
+}