feat(loyalty-discount): implement loyalty and discount system

- Add discount campaign management and validation logic
- Update booking handlers with discount application flow
- Add customer relationship endpoints for loyalty tracking
- Update frontend modals (booking, approval, payment, reschedule)
- Add DiscountsManagement and loyalty reference documentation
- Update dev scripts and database init for discount tables
- Clean up completed plan files

backend/handlers/admin/bookings_test.go

@@ -3121,3 +3121,89 @@ func TestGetBookingsByCreatedRange_OrderedByCreatedAt(t *testing.T) {
 		}
 	}
 }
+
+func TestGetAdminBooking_WithDiscounts(t *testing.T) {
+	resetTestData(t)
+	seedDefaultWorkingHours(t)
+
+	userID, err := fixtures.CreateTestUser(db.DB)
+	if err != nil {
+		t.Fatalf("failed to create test user: %v", err)
+	}
+
+	serviceID, err := fixtures.CreateTestService(db.DB)
+	if err != nil {
+		t.Fatalf("failed to create test service: %v", err)
+	}
+
+	// Create completed booking
+	bookingTime := time.Now().Add(-24 * time.Hour)
+	bookingID := createCompletedBookingWithTimeForAdmin(t, userID, serviceID, bookingTime, 50.00)
+
+	// Create a discount campaign and apply it
+	var campaignID string
+	err = db.DB.QueryRow(context.Background(), `
+		INSERT INTO discount_campaigns (name, campaign_type, discount_percent, status, start_date, end_date)
+		VALUES ($1, 'time_based', 10.0, 'active', NOW() - INTERVAL '2 days', NOW() + INTERVAL '2 days')
+		RETURNING id
+	`, "Admin Test Campaign").Scan(&campaignID)
+	if err != nil {
+		t.Fatalf("failed to create campaign: %v", err)
+	}
+
+	_, err = db.DB.Exec(context.Background(), `
+		INSERT INTO booking_discounts (booking_id, user_id, discount_source, source_id, campaign_type, discount_percent, original_total, discount_amount)
+		VALUES ($1, $2, 'campaign', $3, 'time_based', 10.0, 50.00, 5.00)
+	`, bookingID, userID, campaignID)
+	if err != nil {
+		t.Fatalf("failed to create booking discount: %v", err)
+	}
+
+	// Call GetAdminBookingHandler
+	handler := http.HandlerFunc(bookings.GetAdminBookingHandler)
+	w := makeAdminRequest(handler, "GET", "/api/admin/bookings/"+bookingID, nil)
+
+	if w.Code != http.StatusOK {
+		t.Fatalf("expected status 200, got %d. body: %s", w.Code, w.Body.String())
+	}
+
+	var booking bookings.Booking
+	if err := parseResponseBody(w, &booking); err != nil {
+		t.Fatalf("failed to parse booking: %v", err)
+	}
+
+	if len(booking.Discounts) != 1 {
+		t.Fatalf("expected 1 discount, got %d", len(booking.Discounts))
+	}
+
+	d := booking.Discounts[0]
+	if d.CampaignName == nil || *d.CampaignName != "Admin Test Campaign" {
+		t.Errorf("expected campaign name 'Admin Test Campaign', got %v", d.CampaignName)
+	}
+	if d.DiscountAmount != 5.00 {
+		t.Errorf("expected discount amount 5.00, got %.2f", d.DiscountAmount)
+	}
+}
+
+func createCompletedBookingWithTimeForAdmin(t *testing.T, userID, serviceID string, startTime time.Time, price float64) string {
+	t.Helper()
+	var bookingID string
+	err := db.DB.QueryRow(context.Background(), `
+		INSERT INTO bookings (user_id, start_time, status)
+		VALUES ($1, $2, 'completed')
+		RETURNING id
+	`, userID, startTime).Scan(&bookingID)
+	if err != nil {
+		t.Fatalf("failed to create completed booking: %v", err)
+	}
+
+	_, err = db.DB.Exec(context.Background(), `
+		INSERT INTO booking_services (booking_id, service_id, override_price)
+		VALUES ($1, $2, $3)
+	`, bookingID, serviceID, price)
+	if err != nil {
+		t.Fatalf("failed to link service: %v", err)
+	}
+
+	return bookingID
+}