fix: issue invoice on demand so view-invoice buttons actually work

The admin SPA never called POST /billing/invoices, so every session had
invoice_uuid = null and the view-invoice buttons on the patient services
tab (and MyPatients visit modal) were permanently disabled. Add a shared
useIssueInvoice hook (idempotent create + finalize when draft) and wire
it into:
- DetailsStep: the wizard's final step now really issues the invoice
- SessionServiceCard / PatientDetailPage: clicking view-invoice on a
  session without an invoice issues it first, then opens the summary
- MyPatientsPage visit modal: same, replacing the dead disabled button

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

assets/admin/pages/MyPatientsPage.tsx

@@ -51,6 +51,7 @@ import {
 } from "../lib/patientForm";
 import type { ApiResponse, PaginatedResponse } from "../lib/api";
 import { api } from "../lib/api";
+import { useIssueInvoice } from "../hooks/useIssueInvoice";
 import {
     formatDate,
     formatDateTime,
@@ -210,6 +211,16 @@ function MyPatientsPageInner() {
     >("visits");
     const [expandedVisit, setExpandedVisit] = useState<string | null>(null);
     const [invoiceUuid, setInvoiceUuid] = useState<string | null>(null);
+
+    // «مشاهده فاکتور»: نبودِ invoice_uuid یعنی اول صادر شود (idempotent create + finalize).
+    const issueInvoiceMut = useIssueInvoice(selectedRecord?.uuid);
+    const viewInvoice = (s: PatientSession) => {
+        if (s.invoice_uuid) { setExpandedVisit(null); setInvoiceUuid(s.invoice_uuid); return; }
+        issueInvoiceMut.mutate(s.uuid, {
+            onSuccess: (iv) => { setExpandedVisit(null); setInvoiceUuid(iv); },
+            onError: () => toast.error("صدور فاکتور ناموفق بود"),
+        });
+    };
     const [sessionPage, setSessionPage] = useState(1);
     const [sessionModal, setSessionModal] = useState(false);
     const [editSession, setEditSession] = useState<PatientSession | null>(null);
@@ -1340,7 +1351,8 @@ function MyPatientsPageInner() {
                 onClose={() => setExpandedVisit(null)}
                 settling={settleSessionMut.isPending}
                 onSettle={(uuid) => settleSessionMut.mutate(uuid)}
-                onViewInvoice={(uuid) => { setExpandedVisit(null); setInvoiceUuid(uuid); }}
+                onViewInvoice={viewInvoice}
+                issuing={issueInvoiceMut.isPending}
                 onEdit={(s) => { setExpandedVisit(null); setEditSession(s); }}
             />
 
@@ -1878,6 +1890,7 @@ function VisitDetailModal({
     session,
     onClose,
     settling,
+    issuing,
     onSettle,
     onViewInvoice,
     onEdit,
@@ -1885,8 +1898,10 @@ function VisitDetailModal({
     session: PatientSession | null;
     onClose: () => void;
     settling: boolean;
+    issuing?: boolean;
     onSettle: (uuid: string) => void;
-    onViewInvoice: (uuid: string) => void;
+    /** کل session پاس می‌شود؛ نبودِ invoice_uuid یعنی caller باید فاکتور را صادر کند. */
+    onViewInvoice: (session: PatientSession) => void;
     onEdit: (s: PatientSession) => void;
 }) {
     if (!session) return null;
@@ -1916,11 +1931,9 @@ function VisitDetailModal({
                         <PencilIcon style={{ width: 15 }} /> ویرایش
                     </button>
                     {paid ? (
-                        session.invoice_uuid ? (
-                            <button className="cp-btn-secondary" onClick={() => onViewInvoice(session.invoice_uuid!)}>مشاهده فاکتور</button>
-                        ) : (
-                            <button className="cp-btn-secondary" disabled>پرداخت شده</button>
-                        )
+                        <button className="cp-btn-secondary" disabled={issuing} onClick={() => onViewInvoice(session)}>
+                            {issuing ? 'در حال صدور…' : 'مشاهده فاکتور'}
+                        </button>
                     ) : (
                         <button className="cp-btn-primary" disabled={settling} onClick={() => onSettle(session.uuid)}>تکمیل پرداخت</button>
                     )}