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/main_test.go

@@ -7,16 +7,27 @@ import (
 	"encoding/json"
 	"net/http"
 	"net/http/httptest"
+	"os"
 	"testing"
 
 	"crussell/db"
-	"crussell/testutils"
+	"crussell/testutils/testdb"
 )
 
+func TestMain(m *testing.M) {
+	pool, err := testdb.NewPool("")
+	if err != nil {
+		panic(err)
+	}
+	testdb.Migrate(&testing.T{}, pool)
+	db.DB = pool
+	code := m.Run()
+	pool.Close()
+	os.Exit(code)
+}
+
 func TestHealthCheck_OK(t *testing.T) {
-	// Setup test database
-	cleanup := testutils.SetupTestDB(t)
-	defer cleanup()
+	testdb.TruncateTables(t, db.DB)
 
 	// Create request and recorder
 	req := httptest.NewRequest(http.MethodGet, "/api/health", nil)
@@ -62,10 +73,9 @@ func TestHealthCheck_OK(t *testing.T) {
 }
 
 func TestHealthCheck_Degraded(t *testing.T) {
-	// Setup test database
-	cleanup := testutils.SetupTestDB(t)
+	testdb.TruncateTables(t, db.DB)
 
-	// Save original db.DB and set to nil to simulate degraded state
+	// Set db.DB to nil to simulate degraded state
 	originalDB := db.DB
 	db.DB = nil
 
@@ -105,7 +115,6 @@ func TestHealthCheck_Degraded(t *testing.T) {
 		t.Errorf("expected services.database 'error', got '%v'", services["database"])
 	}
 
-	// Restore original db.DB and cleanup
+	// Restore original db.DB
 	db.DB = originalDB
-	cleanup()
 }