feat: Feature 2 — waiter order cancellation + report updates

Backend:
- Add can_cancel_orders to User model and schema
- Add global orders.waiter_cancellations_allowed setting (migration)
- Cancel endpoints: mark items with cancelled_by/cancelled_at, fire cancellation print
- print_cancellation_ticket: routes to same printer zones, prints ΑΚΥΡΩΣΗ banner
- Fix cancellations_log: date filter, waiter filter, join syntax
- shift/orders: add cancellations count and hours_worked per waiter
- _enrich_shift: add cancellations count to shift data
- Add cancel-permissions endpoint for PWA

Manager dashboard:
- Global cancel setting toggle in Settings > Operation > Shift Settings
- Per-waiter can_cancel_orders checkbox in staff modal
- Manager cancel flow: print confirmation prompt (Ναι/Όχι) in DashboardPage
- ShiftsOverview: Ακυρώσεις column per shift
- Activity: multi-bar chart with ORDERS/ITEMS/CANCELLATIONS/ΕΣΟΔΑ/ΩΡΕΣ checkboxes,
  grouped/stacked switch, right X-axis for hours, full waiter name on hover
- OrderHistory: cancelled items count column per order
- WorkDaySummary drill-down: cancelled items column in orders tab

Waiter PWA:
- Replace 3 pills with CLEAR | ALL | ACTIONS
- ACTIONS opens ItemActionModal for selected items
- ItemActionModal: ORDER AGAIN, MOVE TO OTHER TABLE, SPLIT, CANCEL ORDER
- ActionsSheet: Cancel Παραγγελίας option (greyed if no permission)
- CancelConfirmModal: requires confirmation before cancelling
- TableListPage: cancel order from long-press quick modal

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

local_backend/services/printer_service.py

@@ -1002,6 +1002,90 @@ def print_order_synopsis(ip: str, port: int, synopsis: dict, line_width: int = L
         logger.error("print_order_synopsis failed for %s:%s — %s", ip, port, e)
 
 
+def print_cancellation_ticket(order_id: int, item_ids: List[int]):
+    """
+    Background task: print a ΑΚΥΡΩΣΗ ticket to the same printer zones
+    as the cancelled items. Connects to its own DB session.
+    """
+    db: Session = SessionLocal()
+    try:
+        _do_print_cancellation(order_id, item_ids, db)
+    except Exception as e:
+        logger.exception("Unexpected error in print_cancellation_ticket for order %s: %s", order_id, e)
+    finally:
+        db.close()
+
+
+def _do_print_cancellation(order_id: int, item_ids: List[int], db: Session):
+    if _is_spoof_mode(db):
+        logger.info("Spoof printing ON — dropping cancellation ticket for order %s", order_id)
+        return
+
+    order = db.query(Order).filter(Order.id == order_id).first()
+    if not order:
+        return
+
+    items = db.query(OrderItem).filter(OrderItem.id.in_(item_ids)).all()
+
+    zone_map: dict[int, List[OrderItem]] = {}
+    for item in items:
+        product = db.query(Product).filter(Product.id == item.product_id).first()
+        if product and product.printer_zone_id:
+            zone_map.setdefault(product.printer_zone_id, []).append(item)
+
+    div = load_divider_style(db)
+
+    for printer_id, zone_items in zone_map.items():
+        printer = db.query(Printer).filter(Printer.id == printer_id, Printer.is_active == True).first()
+        if not printer:
+            continue
+        try:
+            p = _get_printer(printer.ip_address, printer.port)
+            _print_cancel_ticket(p, order, zone_items, db, printer.line_width, div)
+            p.close()
+        except Exception as e:
+            logger.error("Cancellation print failed for printer %s: %s", printer.name, e)
+
+
+def _print_cancel_ticket(p: Network, order: Order, items: List[OrderItem], db: Session, line_width: int, div: str):
+    cfg = _load_print_settings(db)
+
+    table_name  = order.table.label or str(order.table.number) if order.table else str(order.table_id)
+    now_str     = _greek_date(datetime.datetime.now(datetime.timezone.utc))
+
+    def _cancel_banner():
+        p._raw(b'\x1b\x61\x01')       # center
+        p._raw(b'\x1b\x21\x30')       # double height+width
+        p._raw(b'\x1b\x45\x01')       # bold on
+        _raw_text(p, "*** AKYPΩΣH ***\n")
+        p._raw(b'\x1b\x45\x00')
+        p._raw(b'\x1b\x21\x00')
+        _divider(p, div, line_width)
+
+    _cancel_banner()
+
+    p._raw(b'\x1b\x61\x00')
+    p._raw(b'\x1b\x21\x10')
+    _raw_text(p, f"Παραγγελια: #{order.id}\n")
+    _raw_text(p, f"Τραπεζι:    {table_name}\n")
+    _raw_text(p, f"Ωρα:        {now_str}\n")
+    p._raw(b'\x1b\x21\x00')
+    _divider(p, div, line_width)
+
+    for item in items:
+        product = db.query(Product).filter(Product.id == item.product_id).first()
+        name = product.name if product else f"#{item.product_id}"
+        p._raw(b'\x1b\x21\x10')
+        _raw_text(p, _item_line(name, item.quantity, line_width) + "\n")
+        p._raw(b'\x1b\x21\x00')
+
+    _divider(p, div, line_width)
+    _cancel_banner()
+
+    p._raw(b'\n\n\n')
+    p.cut()
+
+
 # ── Analytical report prints (products / categories / tables) ─────────────────
 
 def print_products_report(ip: str, port: int, report: dict):