feat(web-admin): sync lump-sum deadline to last due date

Add applyLumpSumDeadlineToLastDueDate for dj payment schedules,
skipping locked or void rows.

Co-authored-by: Cursor <cursoragent@cursor.com>

web-admin/src/utils/protocol-sample-payment.test.ts

@@ -17,7 +17,8 @@ import {
   availableSamplePayModes,
   samplePaymentHasConfirmedTransfer,
   calcLastPeriodDueAmount,
-  shouldAutoFillLastPeriodDue
+  shouldAutoFillLastPeriodDue,
+  applyLumpSumDeadlineToLastDueDate
 } from './protocol-sample-payment'
 
 describe('parsePreferentialPrice', () => {
@@ -372,3 +373,46 @@ describe('shouldAutoFillLastPeriodDue', () => {
     )
   })
 })
+
+describe('applyLumpSumDeadlineToLastDueDate', () => {
+  it('writes deadline to last unlocked schedule', () => {
+    const next = applyLumpSumDeadlineToLastDueDate(
+      [
+        { scheduleNo: 1, dueDate: '', scheduleStatus: 'open' },
+        { scheduleNo: 2, dueDate: '20260101', scheduleStatus: 'open' }
+      ],
+      '20261231',
+      (s) => false
+    )
+    assert.equal(next[0].dueDate, '')
+    assert.equal(next[1].dueDate, '20261231')
+  })
+  it('clears dueDate when deadline empty', () => {
+    const next = applyLumpSumDeadlineToLastDueDate(
+      [{ scheduleNo: 1, dueDate: '20261231', scheduleStatus: 'open' }],
+      '',
+      () => false
+    )
+    assert.equal(next[0].dueDate, '')
+  })
+  it('skips when last schedule locked', () => {
+    const next = applyLumpSumDeadlineToLastDueDate(
+      [{ scheduleNo: 1, dueDate: '20260101', scheduleStatus: 'open' }],
+      '20261231',
+      () => true
+    )
+    assert.equal(next[0].dueDate, '20260101')
+  })
+  it('ignores void schedules when picking last', () => {
+    const next = applyLumpSumDeadlineToLastDueDate(
+      [
+        { scheduleNo: 1, dueDate: '', scheduleStatus: 'open' },
+        { scheduleNo: 2, dueDate: 'old', scheduleStatus: 'void' }
+      ],
+      '20261231',
+      () => false
+    )
+    assert.equal(next[0].dueDate, '20261231')
+    assert.equal(next[1].dueDate, 'old')
+  })
+})