refactor: optimize test DB setup — TestMain per package, truncate-only between tests

- Add TestMain to all 10 test packages (schema DROP+CREATE runs once per package)
- Convert per-test setupTestDB to resetTestData (TRUNCATE only, ~60% faster)
- Add 3 missing tables to TruncateTables (booking_edit_requests, exceptional_group_applications, business_settings)
- Remove dead truncateDiscountTables helper
- Consolidate discount_test.go into package bookings (was external test package)
- Update testutils.SetupTestDB to truncate-only
- Fix unused imports across user, bookings, and handlers packages
- Verify: 286 passing, 2 skipped, 0 failures with -count=2 (no state leakage)

backend/handlers/user/guest_test.go

@@ -21,16 +21,11 @@ import (
 	"net/http/httptest"
 	"strings"
 	"testing"
-
-	"crussell/testutils/jwt"
 )
 
 // TestGuestUser_Create_InvalidPhone verifies that an invalid phone number returns 400 Bad Request.
 func TestGuestUser_Create_InvalidPhone(t *testing.T) {
-	cleanup, _ := setupTest(t)
-	defer cleanup()
-
-	jwt.Init()
+	resetTestData(t)
 
 	reqBody := CreateGuestUserRequest{
 		FirstName: "Test",
@@ -54,10 +49,7 @@ func TestGuestUser_Create_InvalidPhone(t *testing.T) {
 
 // TestGuestUser_Create_EmptyFirstName verifies that an empty first name returns 400 Bad Request.
 func TestGuestUser_Create_EmptyFirstName(t *testing.T) {
-	cleanup, _ := setupTest(t)
-	defer cleanup()
-
-	jwt.Init()
+	resetTestData(t)
 
 	reqBody := CreateGuestUserRequest{
 		FirstName: "",
@@ -81,10 +73,7 @@ func TestGuestUser_Create_EmptyFirstName(t *testing.T) {
 
 // TestGuestUser_Create_NameTooLong verifies that a first name exceeding 50 characters returns 400 Bad Request.
 func TestGuestUser_Create_NameTooLong(t *testing.T) {
-	cleanup, _ := setupTest(t)
-	defer cleanup()
-
-	jwt.Init()
+	resetTestData(t)
 
 	reqBody := CreateGuestUserRequest{
 		FirstName: strings.Repeat("a", 51),
@@ -108,10 +97,7 @@ func TestGuestUser_Create_NameTooLong(t *testing.T) {
 
 // TestGuestUser_Create_InvalidEmail verifies that an invalid email format returns 400 Bad Request.
 func TestGuestUser_Create_InvalidEmail(t *testing.T) {
-	cleanup, _ := setupTest(t)
-	defer cleanup()
-
-	jwt.Init()
+	resetTestData(t)
 
 	reqBody := CreateGuestUserRequest{
 		FirstName: "Test",