feat: Phase 2F — customer CRM

Backend:
- New model: Customer (customers table) — name, nickname, phone, email, notes, is_active
- Order model: add customer_id nullable FK → customers
- New router: /api/customers/ — list (with ?search=), create, get, update, soft-delete,
  GET /{id}/orders (visit history with totals)
- Each CustomerOut includes visit_count + total_spent (computed from closed/paid orders)
- PUT /api/orders/{id}/customer — assign or unassign a customer; manager-only;
  validates customer is active; broadcasts order_updated SSE event
- GET /api/orders/{id} now returns customer_id, customer_name (with nickname), customer_phone
- Migration: CREATE TABLE customers + ALTER TABLE orders ADD COLUMN customer_id

Frontend:
- CustomersPage (/customers): searchable list (name/nickname/phone), avatar initials,
  visit count + total_spent on each row; click → detail panel slides in showing stats
  (visits, total spent, avg ticket), contact info, notes, full visit history
- OrderDetailPage: new Πελάτης card — shows assigned customer in blue if set;
  for open orders shows "+ Ανάθεση πελάτη" button → inline search dropdown → assign;
  Αφαίρεση button to unassign
- Sidebar: Users icon for Πελάτες (between Επαφές and Ρυθμίσεις)

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

local_backend/routers/orders.py

@@ -191,6 +191,15 @@ def get_order(order_id: int, db: Session = Depends(get_db), user: User = Depends
     table = db.query(Table).filter(Table.id == order.table_id).first() if order.table_id else None
     table_name = (table.label or f"T{table.number}") if table else None
 
+    # Phase 2F: resolve customer name for display
+    customer_name = None
+    customer_phone = None
+    if order.customer_id and order.customer:
+        customer_name = order.customer.name
+        if order.customer.nickname:
+            customer_name = f"{order.customer.name} «{order.customer.nickname}»"
+        customer_phone = order.customer.phone
+
     return {
         "id": order.id,
         "table_id": order.table_id,
@@ -202,6 +211,9 @@ def get_order(order_id: int, db: Session = Depends(get_db), user: User = Depends
         "closed_by": order.closed_by,
         "notes": order.notes,
         "business_day_id": order.business_day_id,
+        "customer_id": order.customer_id,
+        "customer_name": customer_name,
+        "customer_phone": customer_phone,
         "items": [fmt_item(i) for i in order.items],
         "waiters": [{"waiter_id": w.waiter_id} for w in order.waiters],
         "audit_logs": [fmt_log(l) for l in order.audit_logs],
@@ -567,6 +579,26 @@ def assign_waiter(order_id: int, body: AssignWaiterRequest, db: Session = Depend
     return {"status": "assigned"}
 
 
+class AssignCustomerBody(BaseModel):
+    customer_id: Optional[int] = None  # null = unassign
+
+
+@router.put("/{order_id}/customer")
+def assign_customer(order_id: int, body: AssignCustomerBody, db: Session = Depends(get_db), user: User = Depends(require_manager)):
+    from models.customers import Customer
+    order = db.query(Order).filter(Order.id == order_id).first()
+    if not order:
+        raise HTTPException(status_code=404, detail="Order not found")
+    if body.customer_id is not None:
+        customer = db.query(Customer).filter(Customer.id == body.customer_id, Customer.is_active == True).first()
+        if not customer:
+            raise HTTPException(status_code=404, detail="Customer not found")
+    order.customer_id = body.customer_id
+    db.commit()
+    broadcast_sync("order_updated", {"order_id": order.id, "table_id": order.table_id, "status": order.status, "action": "customer_assigned"})
+    return {"status": "ok", "customer_id": order.customer_id}
+
+
 @router.delete("/{order_id}/waiters/{waiter_id}", status_code=status.HTTP_204_NO_CONTENT)
 def remove_waiter(order_id: int, waiter_id: int, db: Session = Depends(get_db), user: User = Depends(require_manager)):
     assignment = db.query(OrderWaiter).filter(