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-manager-override.tsx

@@ -193,7 +193,9 @@ export function setDiscountThreshold(pct: number) {
 }
 
 export function requiresDiscountOverride(discountPct: number): boolean {
+  // Check percentage threshold first
   const threshold = getDiscountThreshold()
-  if (threshold <= 0) return requiresOverride('manual_discount')
-  return discountPct >= threshold
+  if (threshold > 0 && discountPct >= threshold) return true
+  // Fall back to the blanket manual_discount toggle
+  return requiresOverride('manual_discount')
 }