Start cash up creates DB record immediately so photo uploads are available

Clicking 'Start Cash Up' now POSTs an empty draft to the backend straight
away, then reloads the record to populate cashUp.id — so PDQ Z-report and
receipt evidence uploaders are available without having to save a draft first.

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

frontend/src/pages/DailyCashUp.tsx

@@ -238,6 +238,27 @@ export function DailyCashUp({ user }: Props) {
     }
   }
 
+  async function startCashUp() {
+    setSaving(true)
+    try {
+      await api.post<{ cash_up_id: number }>('/cashup/save', {
+        session_date: date, status: 'draft', notes: '', checked_transactions: [],
+        denominations: [],
+        card_machines: machines.map(m => ({ name: m.machine_name, total: 0, amex: 0, visa_mc: 0 })),
+      })
+      const data = await api.get<{
+        cash_up: CashUp; denominations: Denomination[]; card_machines: CardMachine[];
+        reconciliation: ReconciliationRow[]; attachments: Attachment[]
+      }>(`/cashup?date=${date}`)
+      applyLoaded(data as { cash_up: CashUp; denominations: Denomination[]; card_machines: CardMachine[]; attachments: Attachment[] })
+    } catch (e: unknown) {
+      flash(e instanceof Error ? e.message : 'Failed to start cash up.', false)
+      setPageState('editing')
+    } finally {
+      setSaving(false)
+    }
+  }
+
   async function save(status: 'draft' | 'final') {
     setSaving(true)
     try {
@@ -331,7 +352,7 @@ export function DailyCashUp({ user }: Props) {
       {pageState === 'empty' && (
         <Card style={{ textAlign: 'center', padding: '2.5rem 1.5rem' }}>
           <p style={{ color: 'var(--text-mid)', marginBottom: '1.25rem' }}>No cash up recorded for this date.</p>
-          <Btn onClick={() => setPageState('editing')}>Start Cash Up</Btn>
+          <Btn onClick={startCashUp} disabled={saving}>{saving ? 'Starting…' : 'Start Cash Up'}</Btn>
         </Card>
       )}