fix: code review fixes + unit/API tests for repair-POS integration

Code review fixes:
- Wrap createFromRepairTicket() in DB transaction for atomicity
- Wrap complete() inventory + status updates in DB transaction
- Repair ticket status update now atomic with transaction completion
- Add Zod validation on from-repair route body
- Fix requiresDiscountOverride: threshold and manual_discount are independent checks
- Order discount distributes proportionally across line items (not first-only)
- Extract shared receipt calculations into useReceiptData/useBarcode hooks
- Add error handling for barcode generation

Tests:
- Unit: consumable tax category mapping, exempt rate short-circuit
- API: ready-for-pickup listing + search, from-repair transaction creation,
  consumable exclusion from line items, tax rate verification (labor=service,
  part=goods), duplicate prevention, ticket auto-pickup on payment completion,
  isConsumable product filter

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

packages/admin/src/components/pos/pos-cart-panel.tsx

@@ -26,6 +26,7 @@ export function POSCartPanel({ transaction }: POSCartPanelProps) {
   const [overrideOpen, setOverrideOpen] = useState(false)
   const [priceItemId, setPriceItemId] = useState<string | null>(null)
   const [pendingDiscount, setPendingDiscount] = useState<{ lineItemId: string; amount: number; reason: string } | null>(null)
+  const [pendingOrderDiscount, setPendingOrderDiscount] = useState<{ amount: number; reason: string } | null>(null)
   const [discountOverrideOpen, setDiscountOverrideOpen] = useState(false)
   const lineItems = transaction?.lineItems ?? []
 
@@ -52,6 +53,28 @@ export function POSCartPanel({ transaction }: POSCartPanelProps) {
     onError: (err) => toast.error(err.message),
   })
 
+  const orderDiscountMutation = useMutation({
+    mutationFn: async ({ amount, reason }: { amount: number; reason: string }) => {
+      // Distribute discount proportionally across all line items
+      let remaining = amount
+      for (let i = 0; i < lineItems.length; i++) {
+        const item = lineItems[i]
+        const itemTotal = parseFloat(item.unitPrice) * item.qty
+        const isLast = i === lineItems.length - 1
+        const share = isLast ? remaining : Math.round((itemTotal / subtotal) * amount * 100) / 100
+        remaining -= share
+        if (share > 0) {
+          await posMutations.applyDiscount(currentTransactionId!, { lineItemId: item.id, amount: share, reason })
+        }
+      }
+    },
+    onSuccess: () => {
+      queryClient.invalidateQueries({ queryKey: posKeys.transaction(currentTransactionId!) })
+      toast.success('Order discount applied')
+    },
+    onError: (err) => toast.error(err.message),
+  })
+
   const voidMutation = useMutation({
     mutationFn: () => posMutations.void(currentTransactionId!),
     onSuccess: () => {
@@ -204,13 +227,13 @@ export function POSCartPanel({ transaction }: POSCartPanelProps) {
               onApply={(amount, reason) => {
                 const pct = subtotal > 0 ? (amount / subtotal) * 100 : 0
                 if (requiresDiscountOverride(pct)) {
-                  setPendingDiscount({ lineItemId: lineItems[0].id, amount, reason })
+                  setPendingOrderDiscount({ amount, reason })
                   setDiscountOverrideOpen(true)
                 } else {
-                  discountMutation.mutate({ lineItemId: lineItems[0].id, amount, reason })
+                  orderDiscountMutation.mutate({ amount, reason })
                 }
               }}
-              isPending={discountMutation.isPending}
+              isPending={orderDiscountMutation.isPending}
             />
           </div>
         )}
@@ -296,6 +319,9 @@ export function POSCartPanel({ transaction }: POSCartPanelProps) {
           if (pendingDiscount) {
             discountMutation.mutate(pendingDiscount)
             setPendingDiscount(null)
+          } else if (pendingOrderDiscount) {
+            orderDiscountMutation.mutate(pendingOrderDiscount)
+            setPendingOrderDiscount(null)
           }
         }}
       />