fix(budget): accept comma decimal separator in expense amounts

The expense Total Amount, per-person "Who paid", and settlement amount
inputs used type="number" with a bare parseFloat. On desktop the number
input normalized comma→dot for free, but mobile keyboards drop the comma
before onChange fires, so parseFloat("39,99") silently became 39.

Switch the three inputs to type="text" inputMode="decimal" and normalize
comma→dot in their onChange handlers, matching the pattern already used
by the other budget inputs (BudgetPanelInlineEditCell, BudgetPanelAddItemRow,
DashboardPage). Both comma and dot now work on every device.

Closes #1256

client/src/components/Budget/CostsPanel.test.tsx

@@ -107,7 +107,7 @@ describe('CostsPanel — settlements in the ledger', () => {
 
     await user.click(await screen.findByRole('button', { name: 'Add expense' }))
     await user.type(await screen.findByPlaceholderText('e.g. Dinner, souvenirs, gas…'), 'Dinner')
-    const nums = () => screen.getAllByRole('spinbutton') as HTMLInputElement[]
+    const nums = () => screen.getAllByPlaceholderText('0.00') as HTMLInputElement[]
     await user.type(nums()[0], '100') // total → auto equal-split across the 2 participants
     await waitFor(() => expect(nums()[1].value).toBe('50'))
     expect(nums()[2].value).toBe('50')
@@ -125,6 +125,30 @@ describe('CostsPanel — settlements in the ledger', () => {
     ]))
   })
 
+  it('accepts a comma as the decimal separator in the total amount (#1256)', async () => {
+    let posted: Record<string, unknown> | null = null
+    server.use(
+      http.get('/api/trips/1/budget', () => HttpResponse.json({ items: [] })),
+      http.get('/api/trips/1/budget/settlement', () => HttpResponse.json({ balances: [], flows: [], settlements: [] })),
+      http.post('/api/trips/1/budget', async ({ request }) => {
+        posted = await request.json() as Record<string, unknown>
+        return HttpResponse.json({ item: { ...buildBudgetItem({ trip_id: 1, name: 'AirTags' }), id: 6 } })
+      }),
+    )
+    const { default: userEvent } = await import('@testing-library/user-event')
+    const user = userEvent.setup()
+    render(<CostsPanel tripId={1} tripMembers={tripMembers} />)
+
+    await user.click(await screen.findByRole('button', { name: 'Add expense' }))
+    await user.type(await screen.findByPlaceholderText('e.g. Dinner, souvenirs, gas…'), 'AirTags')
+    await user.type(screen.getAllByPlaceholderText('0.00')[0], '39,99') // comma → normalized to 39.99
+
+    const addBtns = screen.getAllByRole('button', { name: 'Add expense' })
+    await user.click(addBtns[addBtns.length - 1]) // footer submit
+    await waitFor(() => expect(posted).toBeTruthy())
+    expect(posted!.total_price).toBe(39.99)
+  })
+
   it('marks an expense with no payer as Unfinished', async () => {
     const item = { ...buildBudgetItem({ trip_id: 1, category: 'food', name: 'Hotel' }), total_price: 90, payers: [], members: [{ user_id: 1, username: 'alice', paid: 0 }] }
     server.use(

client/src/components/Budget/CostsPanel.tsx

@@ -754,8 +754,8 @@ function SettlementModal({ tripId, people, me, editing, onClose, onSaved }: {
         </div>
         <div>
           <label className={labelCls}>{t('costs.amount')}</label>
-          <input type="number" inputMode="decimal" min="0" step="0.01" placeholder="0.00" value={amount}
-            onChange={e => setAmount(e.target.value)} className={inputCls} style={{ borderRadius: 10, padding: '11px 13px', fontSize: 14, outline: 'none', fontWeight: 600 }} />
+          <input type="text" inputMode="decimal" placeholder="0.00" value={amount}
+            onChange={e => setAmount(e.target.value.replace(',', '.'))} className={inputCls} style={{ borderRadius: 10, padding: '11px 13px', fontSize: 14, outline: 'none', fontWeight: 600 }} />
         </div>
       </div>
     </Modal>
@@ -833,10 +833,12 @@ export function ExpenseModal({ tripId, base, people, me, editing, prefill, onClo
   }
 
   const onTotalChange = (v: string) => {
+    v = v.replace(',', '.')
     setTotal(v)
     setPaid(prev => rebalance(prev, dirty, participants, parseFloat(v) || 0))
   }
   const onPaidChange = (id: number, v: string) => {
+    v = v.replace(',', '.')
     const nextDirty = new Set(dirty); nextDirty.add(id)
     setDirty(nextDirty)
     setPaid(prev => rebalance({ ...prev, [id]: v }, nextDirty, participants, totalNum))
@@ -896,7 +898,7 @@ export function ExpenseModal({ tripId, base, people, me, editing, prefill, onClo
           <label className={labelCls}>{t('costs.totalAmount')}</label>
           <div className="bg-surface-input border border-edge" style={{ height: FIELD_H, boxSizing: 'border-box', display: 'flex', alignItems: 'center', borderRadius: 10, padding: '0 12px' }}>
             <span className="text-content-faint" style={{ fontSize: 15 }}>{sym(currency)}</span>
-            <input type="number" inputMode="decimal" min="0" step="0.01" placeholder="0.00" value={total}
+            <input type="text" inputMode="decimal" placeholder="0.00" value={total}
               onChange={e => onTotalChange(e.target.value)}
               className="text-content" style={{ flex: 1, border: 0, background: 'none', outline: 'none', fontSize: 15, fontWeight: 600, paddingLeft: 6, width: '100%' }} />
           </div>
@@ -956,7 +958,7 @@ export function ExpenseModal({ tripId, base, people, me, editing, prefill, onClo
                   {on ? (
                     <div className="bg-surface-input border border-edge" style={{ display: 'flex', alignItems: 'center', gap: 4, borderRadius: 8, padding: '0 10px' }}>
                       <span className="text-content-faint" style={{ fontSize: 13 }}>{sym(currency)}</span>
-                      <input type="number" inputMode="decimal" min="0" step="0.01" placeholder="0.00" value={paid[p.id] || ''}
+                      <input type="text" inputMode="decimal" placeholder="0.00" value={paid[p.id] || ''}
                         onChange={e => onPaidChange(p.id, e.target.value)}
                         className="text-content" style={{ width: '100%', border: 0, background: 'none', outline: 'none', fontSize: 14, fontWeight: 600, padding: '8px 0', textAlign: 'right' }} />
                     </div>