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.

Helpers/BookingInvoiceHtml.cs

@@ -0,0 +1,68 @@
+using Fitness_core_BE.DTOs.Booking;
+using System.Net;
+
+namespace Fitness_core_BE.Helpers
+{
+    // Minimal, dependency-free HTML receipt for a booking payment -- mirrors BookingViewHtml.cs's
+    // "self-contained page, share the link" pattern, kept as its own file since a receipt's
+    // content (itemized charge, payment method) is different enough from the booking confirmation
+    // page to not share a template.
+    public static class BookingInvoiceHtml
+    {
+        public static string Render(BookingInvoiceDto invoice)
+        {
+            var when = $"{invoice.BookingStartTime:dddd, dd MMM yyyy}, {invoice.BookingStartTime:h:mm tt} - {invoice.BookingEndTime:h:mm tt}";
+
+            return $$"""
+                <!DOCTYPE html>
+                <html lang="en">
+                <head>
+                  <meta charset="utf-8" />
+                  <meta name="viewport" content="width=device-width, initial-scale=1" />
+                  <title>Payment Receipt - Vijaya Sport Club</title>
+                  <style>
+                    body { font-family: -apple-system, Segoe UI, Roboto, Arial, sans-serif; background: #f3f4f6; margin: 0; padding: 24px 16px; color: #111827; }
+                    .card { max-width: 420px; margin: 0 auto; background: #fff; border-radius: 12px; box-shadow: 0 1px 3px rgba(0,0,0,0.1); overflow: hidden; }
+                    .header { background: #0f172a; color: #fff; padding: 20px; }
+                    .header h1 { margin: 0; font-size: 18px; }
+                    .body { padding: 20px; }
+                    .row { display: flex; justify-content: space-between; padding: 8px 0; border-bottom: 1px solid #f1f5f9; }
+                    .row .label { color: #6b7280; font-size: 13px; }
+                    .row .value { font-weight: 600; font-size: 13px; text-align: right; }
+                    .total { margin-top: 16px; text-align: center; background: #f8fafc; border: 1px dashed #cbd5e1; border-radius: 8px; padding: 16px; }
+                    .total-label { font-size: 12px; color: #6b7280; margin-bottom: 6px; }
+                    .total-amount { font-size: 28px; font-weight: 700; color: #0f172a; }
+                  </style>
+                </head>
+                <body>
+                  <div class="card">
+                    <div class="header"><h1>Vijaya Sport Club — Receipt</h1></div>
+                    <div class="body">
+                      <div class="row"><span class="label">Facility</span><span class="value">{{Encode(invoice.FacilityName)}}</span></div>
+                      <div class="row"><span class="label">Session</span><span class="value">{{Encode(when)}}</span></div>
+                      <div class="row"><span class="label">Paid by</span><span class="value">{{Encode(invoice.GuestName)}}</span></div>
+                      <div class="row"><span class="label">Payment Method</span><span class="value">{{Encode(invoice.PaymentMethod)}}</span></div>
+                      <div class="row"><span class="label">Issued</span><span class="value">{{invoice.IssuedAt:dd MMM yyyy, h:mm tt}}</span></div>
+                      <div class="total">
+                        <div class="total-label">Amount Paid</div>
+                        <div class="total-amount">Rs. {{invoice.Amount:N2}}</div>
+                      </div>
+                    </div>
+                  </div>
+                </body>
+                </html>
+                """;
+        }
+
+        public static string NotFound() => """
+            <!DOCTYPE html>
+            <html><head><meta charset="utf-8" /><title>Receipt not found</title></head>
+            <body style="font-family: sans-serif; text-align: center; padding: 60px 20px; color: #6b7280;">
+              <h2>Receipt not found</h2>
+              <p>This link may be invalid.</p>
+            </body></html>
+            """;
+
+        private static string Encode(string? value) => WebUtility.HtmlEncode(value ?? "");
+    }
+}