feat(last-mile): customer-signed LM contract gates the advance invoice

Approval now snapshots the rate estimate and generates a last-mile
contract instead of invoicing immediately. The customer picks a delivery
date on the confirm form, then reviews and signs the contract in the
portal (saved signature or drawn); the signed PDF is stored as
LM_<CustomerName>.pdf and only then is the advance invoice issued.
Backoffice shows signature status and the contract download.

apps/edr-freight-web/backoffice/src/services/last-mile-requests.service.ts

@@ -28,6 +28,9 @@ export interface LastMileRequest {
   reviewedAt?: string | null;
   rejectionReason?: string | null;
   resultingLastMileId?: string | null;
+  requestedDeliveryDate?: string | null;
+  customerSignedAt?: string | null;
+  signerDisplayName?: string | null;
   createdAt: string;
   updatedAt: string;
 }
@@ -58,4 +61,6 @@ export const lastMileRequestsService = {
     api.post<LastMileRequest>(LMR.APPROVE(id), { advanceAmount }),
   reject: (id: string, reason: string) =>
     api.post<LastMileRequest>(LMR.REJECT(id), { reason }),
+  contractDocument: (id: string) =>
+    api.get<Blob>(LMR.CONTRACT_DOCUMENT(id), { responseType: 'blob' }),
 };