fix: shift closing total reflects money collected, not invoiced

[NotAbdelrahmanelsayed]

Problem

When closing a POS shift, the closing total counts the full grand total of every invoice linked to the shift — even pure Pay-on-Account credit sales where no money was received. The cash Payment Reconciliation is built only from real payment rows, so it is already correct — but Net Sales (grand_total) disagrees with it within a single shift:

Event	Cash reconciliation	Net Sales (grand_total)
Credit sale created (no money)	+0 (correct)	+full amount (bug)
Old due collected today	+amount (correct)	+0

Root cause: pos_closing_shift.py › _process_invoice() added base_grand_total (the full invoice value) into grand_total/net_total/sales_total and the per-row amount, ignoring how much was actually paid.

Fix

For non-return invoices, the money summaries and the per-row grand_total now use the amount actually collected (base_paid_amount):

• pure credit sale → contributes 0
• partial sale → contributes only its down-payment
• net_total scaled by paid_ratio = base_paid / base_grand_total

The full invoice value is preserved in transaction_amount; display-only invoice_total and outstanding_amount are added for the dialog and stripped before the child-table set (Sales Invoice Reference has no such columns). Quantities, tax accrual and the returns branch are unchanged. With this change Net Sales == sum of per-invoice collected == reconciliation cash delta.

The Close Shift dialog shows an On Account / Partially Paid badge and an Unpaid: {amount} sub-line on rows collected for less than their invoice value (desktop + mobile).

Edge case: if a credit sale is created and its due is collected within the same shift, the down-payment shows in Net Sales and the later dues Payment Entry shows in reconciliation — both are real takings, reported in their respective sections.

Tests

Adds unit tests for _process_invoice covering fully-paid, pure-credit, partial and credit-return cases, asserting the summary equals only the collected portions and per-row amounts sum to the header total. Adds the Arabic translation for the new Unpaid: {0} string.

🤖 Generated with Claude Code

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This pull request has been automatically marked as stale because it has not had recent activity for 21 days.

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[MostafaKadry]

Nice fix @NotAbdelrahmanelsayed!, this closes a real gap between Net Sales and what's actually in the drawer. Two things I found while testing that are worth patching before merge:

1. change_amount isn't netted out of "collected" (_process_invoice):
   paid_amount is the raw sum of tendered payment rows, not net of change. So a $15.50 sale paid with a $20 bill ($4.50 change) currently computes collected = 20, not 15.50. Net Sales gets inflated by every cash-with-change sale, and outstanding_amount goes negative instead of 0.

Fix: subtract change before it's used anywhere:
base_change = get_base_value(invoice, "change_amount", "base_change_amount", conversion_rate)
base_paid = get_base_value(invoice, "paid_amount", "base_paid_amount", conversion_rate) - base_change
paid_ratio = (base_paid / base_grand_total) if base_grand_total else 0
(you already compute base_change further down for the cash-reconciliation bucket — just hoist that one line up and reuse it, no need to compute it twice.)

2. Taxes stayed accrual-basis, everything else went cash-basis

net_total/grand_total now scale by paid_ratio for partial/credit sales, but the tax loop still aggregates the full tax_amount regardless of what was collected. That breaks grand_total ≈ net_total + taxes for any shift with a partial/credit sale that has tax on it. Worth a deliberate call. I'd scale it too, for consistency:
tax_ratio = 1 if is_return else paid_ratio
for t in invoice.taxes:
tax_amount = get_base_value(t, "tax_amount", "base_tax_amount", conversion_rate) * tax_ratio
_aggregate_tax(taxes, t.account_head, t.rate, tax_amount)

One unrelated nit: test_pos_closing_shift.py is 4-space indented. repo convention is tabs (ruff format will flag it).