fix: report cancellation bugs + missing OrderItem model columns

Backend:
- OrderItem model: add cancelled_at, cancelled_by, cancel_reason columns
  (migration existed but model was missing them — caused 500 on cancellations_log)
- shifts.py _enrich_shift: count cancellations by quantity sum (not row count),
  add cancellation_value (sum of unit_price * quantity)
- reports.py current business day: add cancelled_items count (per-item quantity sum,
  across all orders in the day, not just fully-cancelled orders)

Manager dashboard:
- PrintFontsTab: fix SSE auth token key (access_token → manager_token, was causing 403)
- Today: show cancelled_items count as sub-label on Ακυρώσεις stat card
- OrderHistory: items/cancellations columns now use quantity sum, not row count
- WorkDaySummary drill-down: same quantity-sum fix
- ShiftsOverview: add Αξία Ακυρ. column next to Ακυρώσεις

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

local_backend/routers/reports.py

@@ -1260,6 +1260,16 @@ def current_business_day(
         p = db.query(Product).filter(Product.id == top_product_id).first()
         top_product = {"id": top_product_id, "name": p.name if p else f"#{top_product_id}", "qty": item_counts[top_product_id]}
 
+    # Count cancelled items (individual items cancelled, across all orders in this day)
+    all_order_ids = [o.id for o in orders]
+    cancelled_items_qty = 0
+    if all_order_ids:
+        from sqlalchemy import func as sqlfunc
+        cancelled_items_qty = db.query(sqlfunc.sum(OrderItem.quantity)).filter(
+            OrderItem.order_id.in_(all_order_ids),
+            OrderItem.status == "cancelled",
+        ).scalar() or 0
+
     return {
         "business_day": {
             "id": day.id,
@@ -1272,6 +1282,7 @@ def current_business_day(
             "orders_open": len(open_orders),
             "active_waiters": len(active_shifts),
             "cancellations": len(cancelled_orders),
+            "cancelled_items": int(cancelled_items_qty),
             "top_product": top_product,
         }
     }