fix: S3-dependent tests skip in prod, add GO_TESTING to CI for dav init

backend/handlers/user/profile_test.go

@@ -29,6 +29,7 @@ import (
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 
+	"crussell/internal/s3"
 	"crussell/mw"
 	"crussell/testutils"
 	"crussell/testutils/fixtures"
@@ -1226,6 +1227,10 @@ func TestProcessProfileImage_InvalidImage(t *testing.T) {
 // =============================================================================
 
 func TestUploadProfilePicture_Success(t *testing.T) {
+	if s3.Client == nil {
+		t.Skip("S3 client not initialized (requires R2_ENDPOINT)")
+	}
+
 	ctx, tx := testutils.SetupTestTx(t)
 
 	userID, err := fixtures.CreateTestUser(tx)
@@ -1291,6 +1296,10 @@ func TestUploadProfilePicture_NoAuth(t *testing.T) {
 }
 
 func TestUploadProfilePicture_NotImage(t *testing.T) {
+	if s3.Client == nil {
+		t.Skip("S3 client not initialized (requires R2_ENDPOINT)")
+	}
+
 	ctx, tx := testutils.SetupTestTx(t)
 
 	userID, err := fixtures.CreateTestUser(tx)