feat: Enhance booking functionality with invoice management and dashboard summary

- Added customerId to guest booking requests for better identification.
- Implemented new endpoints for managing booking invoices and dashboard summaries.
- Created BookingInvoice and BookingDashboardSummary DTOs to support new features.
- Updated Booking and BookingInvoice models to include payment method and timestamps.
- Enhanced BookingService to handle invoice creation upon payment confirmation.
- Modified BookingRepository to support CRUD operations for BookingInvoice.
- Updated TenantDbContext to include BookingInvoice DbSet and relevant configurations.
- Improved error handling and validation for booking completion and payment processes.

Models/BookingInvoice.cs

@@ -0,0 +1,44 @@
+using System.ComponentModel.DataAnnotations;
+using System.ComponentModel.DataAnnotations.Schema;
+
+namespace Fitness_core_BE.Models
+{
+    /// <summary>A snapshot receipt generated the moment a Booking's payment is recorded (either
+    /// via MarkGuestBookingPaid or the Complete checkout flow) -- deliberately NOT a live join to
+    /// Booking/Facility, so it stays stable and printable even if the booking is later reassigned,
+    /// rescheduled, or the facility renamed. Purpose-built for bookings and kept entirely separate
+    /// from CustomerInvoice, which is hardwired to the membership/subscription domain
+    /// (FKCustomerSubscriptionId is required there) and has no concept of a one-off booking
+    /// charge.</summary>
+    public class BookingInvoice
+    {
+        [Key]
+        public Guid BookingInvoiceId { get; set; }
+
+        public Guid FKBookingId { get; set; }
+        [ForeignKey(nameof(FKBookingId))]
+        public Booking? Booking { get; set; }
+
+        public Guid FKClientId { get; set; }
+        [ForeignKey(nameof(FKClientId))]
+        public Client Client { get; set; }
+
+        public decimal Amount { get; set; }
+
+        /// <summary>"Cash" | "Bank".</summary>
+        [MaxLength(20)]
+        public string PaymentMethod { get; set; } = "Cash";
+
+        [MaxLength(200)]
+        public string GuestName { get; set; } = string.Empty;
+        [MaxLength(32)]
+        public string? GuestPhone { get; set; }
+
+        [MaxLength(128)]
+        public string FacilityName { get; set; } = string.Empty;
+        public DateTime BookingStartTime { get; set; }
+        public DateTime BookingEndTime { get; set; }
+
+        public DateTime IssuedAt { get; set; } = DateTime.UtcNow;
+    }
+}