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.

DTOs/Booking/BookingInvoiceDto.cs

@@ -0,0 +1,21 @@
+namespace Fitness_core_BE.DTOs.Booking
+{
+    /// <summary>A booking payment receipt -- deliberately separate from the membership-based
+    /// CustomerInvoice, listed on its own "Invoices" tab, not mixed into Customer Payments.</summary>
+    public class BookingInvoiceDto
+    {
+        public Guid BookingInvoiceId { get; set; }
+        public Guid BookingId { get; set; }
+        public decimal Amount { get; set; }
+        public string PaymentMethod { get; set; } = string.Empty;
+        public string GuestName { get; set; } = string.Empty;
+        public string? GuestPhone { get; set; }
+        public string FacilityName { get; set; } = string.Empty;
+        public DateTime BookingStartTime { get; set; }
+        public DateTime BookingEndTime { get; set; }
+        public DateTime IssuedAt { get; set; }
+
+        /// <summary>Public, unauthenticated link to this receipt's printable page.</summary>
+        public string? ShareUrl { get; set; }
+    }
+}