feat(orders): per-item kitchen/bar notes (POS + QR app + KDS)

Lets the POS agent and the QR/app customer attach a free-text note to each
order line (e.g. "no tomato", "extra hot") that reaches the kitchen/bar.

- Backend already supported it (OrderItem.Notes persists; CreateOrderItemRequest
  and OrderItemDto carry Notes; LiveOrderDto items include it) — this wires the UI.
- cart.store: add setNotes(menuItemId, notes); notes already travel in
  getPendingLines and round-trip via hydrateFromOrder.
- POS pos-screen: a note input under each cart line.
- QR guest menu: a note input under each cart line (QrCartLine.note).
- KDS: render the note prominently under each item so kitchen/bar sees it.
- i18n: pos.itemNotePlaceholder + qrMenu.itemNote (fa/ar/en).

Note: notes are captured on items being added; editing a note on an
already-submitted line is out of scope (no pending delta to re-send).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

web/dashboard/src/lib/stores/cart.store.ts

@@ -34,6 +34,7 @@ interface CartState {
   addItem: (item: MenuItem) => void;
   removeItem: (menuItemId: string) => void;
   updateQty: (menuItemId: string, quantity: number) => void;
+  setNotes: (menuItemId: string, notes: string) => void;
   setCouponCode: (code: string) => void;
   setAppliedCoupon: (coupon: AppliedCoupon | null) => void;
   clearCoupon: () => void;
@@ -135,6 +136,13 @@ export const useCartStore = create<CartState>((set, get) => ({
     });
   },
 
+  setNotes: (menuItemId, notes) =>
+    set({
+      items: get().items.map((i) =>
+        i.menuItem.id === menuItemId ? { ...i, notes: notes.trim() || undefined } : i
+      ),
+    }),
+
   setCouponCode: (code) => set({ couponCode: code }),
   setAppliedCoupon: (coupon) => set({ appliedCoupon: coupon }),
   clearCoupon: () => set(clearCouponState),