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/test_helpers.go

@@ -9,48 +9,19 @@ import (
 	"encoding/json"
 	"net/http"
 	"net/http/httptest"
-	"os"
 	"testing"
 
 	"crussell/db"
 	"crussell/mw"
-	"crussell/testutils/jwt"
 	"crussell/testutils/testdb"
 
 	"github.com/go-chi/chi/v5"
 )
 
-// TestMain initializes test environment variables before any tests run
-func TestMain(m *testing.M) {
-	// Set database environment variables for test database
-	os.Setenv("POSTGRES_USER", "myuser")
-	os.Setenv("POSTGRES_PASSWORD", "mypassword")
-	os.Setenv("POSTGRES_HOST", "localhost")
-	os.Setenv("POSTGRES_DB", "crussell_test")
-	os.Setenv("GO_TESTING", "true")
-
-	// Run the tests
-	code := m.Run()
-	os.Exit(code)
-}
-
-// setupTestDB replaces the global db.DB with a test pool and returns a cleanup function
-func setupTestDB(t *testing.T) func() {
+// resetTestData truncates tables to clean up data between tests
+func resetTestData(t *testing.T) {
 	t.Helper()
-
-	pool := testdb.Pool(t)
-	testdb.Migrate(t, pool)
-	testdb.TruncateTables(t, pool) // Clear data between tests
-
-	originalDB := db.DB
-	db.DB = pool
-
-	jwt.Init()
-
-	return func() {
-		db.DB = originalDB
-		pool.Close()
-	}
+	testdb.TruncateTables(t, db.DB)
 }
 
 // makeAdminRequest creates a request with admin context