refactor(backend): replace resetTestData with SetupTestDB and add new tests

Migrate all test files from resetTestData(t) to testutils.SetupTestDB(t) for isolated per-package test databases.

- Add new feature tests: name history assertions, referral discount preview,
  time blockers, email validation, GDPR export, loyalty manual redemption
- Update existing tests to use batch queries and SetupTestDB
- Remove test_helpers.go resetTestData infrastructure
- Add comprehensive user profile tests (442 new lines)

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

backend/handlers/services/services_test.go

@@ -17,39 +17,17 @@ import (
 	"bytes"
 	"context"
 	"encoding/json"
-	"fmt"
 	"net/http"
 	"net/http/httptest"
-	"os"
 	"testing"
 
 	"crussell/db"
+	"crussell/testutils"
 	"crussell/handlers/user"
-	"crussell/testutils/jwt"
-	"crussell/testutils/testdb"
 
 	"github.com/go-chi/chi/v5"
 )
 
-func TestMain(m *testing.M) {
-	pool, err := testdb.NewPool("")
-	if err != nil {
-		fmt.Println("failed to create pool:", err)
-		os.Exit(1)
-	}
-	testdb.Migrate(&testing.T{}, pool)
-	db.DB = pool
-	jwt.Init()
-	code := m.Run()
-	pool.Close()
-	os.Exit(code)
-}
-
-func resetTestData(t *testing.T) {
-	t.Helper()
-	testdb.TruncateTables(t, db.DB)
-}
-
 // createUserWithDOB creates a test user with specified date of birth
 func createUserWithDOB(dob string) (string, error) {
 	ctx := context.Background()
@@ -117,7 +95,7 @@ func findLastSegment(path, prefix string) int {
 // TestServices_ListAll verifies that listing all services returns only active services,
 // filtering out inactive services from the response.
 func TestServices_ListAll(t *testing.T) {
-	resetTestData(t)
+	testutils.SetupTestDB(t)
 
 	_, err := db.DB.Exec(context.Background(), `
 		INSERT INTO services (name, description, price, duration_minutes, is_active, minimum_age_required)
@@ -164,7 +142,7 @@ func TestServices_ListAll(t *testing.T) {
 // TestServices_EligibleForUser_AgeFilter verifies that eligible services are filtered based on the user's age,
 // excluding services with minimum_age_required higher than the user's age.
 func TestServices_EligibleForUser_AgeFilter(t *testing.T) {
-	resetTestData(t)
+	testutils.SetupTestDB(t)
 
 	dob := "2006-01-01" // Age 20 in Feb 2026
 	userID, err := createUserWithDOB(dob)
@@ -218,7 +196,7 @@ func TestServices_EligibleForUser_AgeFilter(t *testing.T) {
 // TestServices_EligibleForUser_PatchTest verifies that services requiring patch tests include a
 // PatchTestStatus field set to 'ok' when the user has completed a valid patch test for that service.
 func TestServices_EligibleForUser_PatchTest(t *testing.T) {
-	resetTestData(t)
+	testutils.SetupTestDB(t)
 
 	dob := "2000-01-01"
 	userID, err := createUserWithDOB(dob)
@@ -312,7 +290,7 @@ func TestServices_EligibleForUser_PatchTest(t *testing.T) {
 // TestContact_ReturnsInfo verifies that the contact info endpoint returns the salon's contact
 // details (name, phone, email, role) from the first admin user in the database.
 func TestContact_ReturnsInfo(t *testing.T) {
-	resetTestData(t)
+	testutils.SetupTestDB(t)
 
 	_, err := db.DB.Exec(context.Background(), `
 		INSERT INTO users (n_first_name, n_last_name, email, phone, date_of_birth, password_hash, account_role, account_type)