Fix billing data integrity, sale atomicity and stock safety

Bills were persisted correctly but read back wrong. The read path rebuilt a
cart from its lines alone, dropping bill-level discounts and loyalty, so every
figure derived from a stored bill was overstated: the upload payload, the day
archive and the shift report. A discounted 529 bill read back as 620.

Money and data integrity
- order_dao: restore bill_discount and points_redeemed when rebuilding a cart;
  keep the reconstruction tier-less so the membership discount is not applied
  twice. Trust the recorded total and points via SaleTransaction.storedTotal.
- checkout_sale + order_dao.commitSale: write the bill, its stock movement and
  the loyalty update in one transaction. Previously a failure part-way through
  left a persisted bill the cashier believed had failed, inviting a duplicate.
- checkout_sale: re-check every line against live stock. A parked bill resumed
  after its stock was sold passed validation and oversold.
- catalogue_dao: allocate the invoice sequence in one transaction; the previous
  read-modify-write could hand two sales the same number and fail UNIQUE.
- local_store: replay unsynced sales after a catalogue import, so a mid-shift
  re-import cannot restore stock that has already been sold.
- payment_controller: stamp the signed-in operator on the bill instead of the
  hardcoded seed session, and pass the terminal id through.
- cart: reconcile per-slab GST against the bill total so the parts sum to the
  whole on a tax invoice.

Sync and reporting
- sync_repository: drain unsynced bills in a loop rather than silently capping
  at one page; stop on rejection so rejected rows cannot loop forever.
- sync_log_dao (new): persist the sync history to the sync_log table, which the
  schema already defined but nothing used. It was in memory, so the only record
  that bills had been uploaded died at restart.
- Scope shift reports by cashier. day_archive is re-keyed to
  (business_date, cashier_name) so a till stays settleable after its bills are
  uploaded and deleted. Schema v4 with a migration that carries v3 rows across.

Input and UI
- barcode_service: consume machine-paced keystrokes so a scan cannot also land
  in the focused field, and raise the bar to 60ms/char while a text field has
  focus so typing a mobile number is not read as a scan. Clock and focus check
  injected so the behaviour is testable.
- primary_button: make the label flexible; label plus trailing total overflowed
  the Charge button by up to 131px.
- app_router: redirect instead of null-casting when the receipt route is
  entered without its transaction.
- customer_repository: reduce the search query to digits so a punctuated mobile
  number matches.

Cleanup
- Remove TransactionRepository.save, CustomerRepository.recordSale and
  OrderDao.insertOrder, all superseded by commitSale.
- dart fix across the tree; 251 analyzer issues down to 3 info-level.

Tests: 23 passing / 15 failing -> 90 passing. Fixed the two defects that broke
the existing suite (containsAll type argument, reset() needing a catalogue) and
deleted the leftover template test. Added coverage for the order round trip,
the day archive after a real sync, stock safety, checkout atomicity, the v3->v4
migration, scanner-versus-human input, and an app-level smoke test that renders
every module.

Note: bills already uploaded with a discount went up overstated. This stops it
happening again but does not correct historical server data.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

lib/domain/usecases/checkout_sale.dart

@@ -51,10 +51,33 @@ class CheckoutSale {
     required Cart cart,
     required List<PaymentSplit> payments,
     required String cashierName,
+    String terminalId = 'TERM-01',
   }) async {
     _validate(cart, payments);
+    await _assertStockAvailable(cart);
 
     final now = DateTime.now();
+
+    // The shopper's new balance is computed before anything is written, so it
+    // can be persisted in the same transaction as the bill.
+    Customer? updatedCustomer;
+    final customer = cart.customer;
+    if (customer != null) {
+      final current = await _customers.findById(customer.id);
+      if (current == null) {
+        throw const CheckoutFailure(
+          'This customer is no longer on file. Remove them from the bill to '
+          'continue.',
+        );
+      }
+      updatedCustomer = current.applySale(
+        amount: cart.grandTotal,
+        pointsEarned: cart.pointsEarned,
+        pointsRedeemed: cart.pointsRedeemed,
+        at: now,
+      );
+    }
+
     final sequence = await _transactions.nextInvoiceSequence();
 
     final transaction = SaleTransaction(
@@ -64,24 +87,16 @@ class CheckoutSale {
       payments: payments,
       createdAt: now,
       cashierName: cashierName,
+      terminalId: terminalId,
     );
 
-    await _transactions.save(transaction);
-
-    await _products.decrementStock({
-      for (final line in cart.lines) line.product.id: line.quantity,
-    });
-
-    Customer? updatedCustomer;
-    final customer = cart.customer;
-    if (customer != null) {
-      updatedCustomer = await _customers.recordSale(
-        customerId: customer.id,
-        amount: cart.grandTotal,
-        pointsEarned: cart.pointsEarned,
-        pointsRedeemed: cart.pointsRedeemed,
-      );
-    }
+    await _transactions.commitSale(
+      transaction: transaction,
+      stockMovements: {
+        for (final line in cart.lines) line.product.id: line.quantity,
+      },
+      updatedCustomer: updatedCustomer,
+    );
 
     return CheckoutResult(
       transaction: transaction,
@@ -89,6 +104,29 @@ class CheckoutSale {
     );
   }
 
+  /// Re-checks every line against live stock.
+  ///
+  /// [CartLine.exceedsStock] reads the product snapshot taken when the item was
+  /// added, which goes stale the moment anything else sells the same item — a
+  /// parked bill resumed after its stock was sold would otherwise pass
+  /// validation and oversell.
+  Future<void> _assertStockAvailable(Cart cart) async {
+    for (final line in cart.lines) {
+      final live = await _products.findById(line.product.id);
+      if (live == null) {
+        throw CheckoutFailure(
+          '${line.product.name} is no longer in the catalogue.',
+        );
+      }
+      if (line.quantity > live.stock) {
+        throw CheckoutFailure(
+          'Only ${live.stock.toStringAsFixed(0)} ${live.unit.symbol} of '
+          '${live.name} in stock.',
+        );
+      }
+    }
+  }
+
   void _validate(Cart cart, List<PaymentSplit> payments) {
     if (cart.isEmpty) {
       throw const CheckoutFailure('Add at least one item before charging.');