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/admin/users_test.go

@@ -29,8 +29,7 @@ import (
 // TestAdminUsers_List verifies that an admin can list all users in the
 // system with their details including account role and type.
 func TestAdminUsers_List(t *testing.T) {
-	cleanup := setupTestDB(t)
-	defer cleanup()
+	resetTestData(t)
 
 	// Create test users
 	_, err := db.DB.Exec(context.Background(), `
@@ -68,8 +67,7 @@ func TestAdminUsers_List(t *testing.T) {
 // TestAdminUsers_Get tests that an admin can retrieve detailed information
 // about a specific user including their profile and account settings.
 func TestAdminUsers_Get(t *testing.T) {
-	cleanup := setupTestDB(t)
-	defer cleanup()
+	resetTestData(t)
 
 	// Create test user
 	var userID string
@@ -106,8 +104,7 @@ func TestAdminUsers_Get(t *testing.T) {
 // TestAdminUsers_Get_NotFound verifies that requesting details for a
 // non-existent user returns HTTP 404 Not Found.
 func TestAdminUsers_Get_NotFound(t *testing.T) {
-	cleanup := setupTestDB(t)
-	defer cleanup()
+	resetTestData(t)
 
 	handler := http.HandlerFunc(user.GetAdminUserHandler)
 	// Use 12-char or less ID to avoid CHAR(12) constraint error
@@ -122,8 +119,7 @@ func TestAdminUsers_Get_NotFound(t *testing.T) {
 // identifies which services require patch tests and returns only those services
 // the user is eligible for based on age requirements.
 func TestAdminUsers_PatchTests_Eligible(t *testing.T) {
-	cleanup := setupTestDB(t)
-	defer cleanup()
+	resetTestData(t)
 
 	// Create test user
 	var userID string
@@ -199,8 +195,7 @@ func TestAdminUsers_PatchTests_Eligible(t *testing.T) {
 // user already has a valid patch test on file, that service is filtered out
 // from the eligible list (since they've already completed it).
 func TestAdminUsers_PatchTests_Eligible_WithExisting(t *testing.T) {
-	cleanup := setupTestDB(t)
-	defer cleanup()
+	resetTestData(t)
 
 	// Create test user
 	var userID string
@@ -286,8 +281,7 @@ func TestAdminUsers_PatchTests_Eligible_WithExisting(t *testing.T) {
 // TestAdminUsers_AddPatchTest verifies that an admin can record a patch
 // test completion for a user, creating a user_patch_tests record.
 func TestAdminUsers_AddPatchTest(t *testing.T) {
-	cleanup := setupTestDB(t)
-	defer cleanup()
+	resetTestData(t)
 
 	// Create test user
 	var userID string
@@ -346,8 +340,7 @@ func TestAdminUsers_AddPatchTest(t *testing.T) {
 }
 
 func TestAdminUsers_AddPatchTest_InvalidPatchTest(t *testing.T) {
-	cleanup := setupTestDB(t)
-	defer cleanup()
+	resetTestData(t)
 
 	// Create test user
 	var userID string
@@ -374,8 +367,7 @@ func TestAdminUsers_AddPatchTest_InvalidPatchTest(t *testing.T) {
 // TestAdminUsers_NonAdmin verifies that non-admin users receive HTTP 403
 // Forbidden when attempting to list users, get user details, or manage patch tests.
 func TestAdminUsers_NonAdmin(t *testing.T) {
-	cleanup := setupTestDB(t)
-	defer cleanup()
+	resetTestData(t)
 
 	// Create regular user in DB
 	_, err := db.DB.Exec(context.Background(), `
@@ -429,8 +421,7 @@ func TestAdminUsers_NonAdmin(t *testing.T) {
 // TestAdminUsers_Get_Success is an additional test verifying admin can
 // retrieve user details including ID, name, email, and account role.
 func TestAdminUsers_Get_Success(t *testing.T) {
-	cleanup := setupTestDB(t)
-	defer cleanup()
+	resetTestData(t)
 
 	// Create a test user
 	var userID string
@@ -478,8 +469,7 @@ func TestAdminUsers_Get_Success(t *testing.T) {
 // TestAdminUsers_AddPatchTest_Duplicate verifies that recording the same patch test
 // twice updates the tested_at timestamp (upsert behavior).
 func TestAdminUsers_AddPatchTest_Duplicate(t *testing.T) {
-	cleanup := setupTestDB(t)
-	defer cleanup()
+	resetTestData(t)
 
 	// Create test user
 	var userID string