fix: use targeted DELETE in DAV test instead of full table wipe

backend/internal/dav/shared_test.go

@@ -89,7 +89,7 @@ func TestGetContactByURI_NotFound(t *testing.T) {
 func TestListAllContacts_Empty(t *testing.T) {
 	ctx := context.Background()
 
-	_, err := testSvc.db.Exec(ctx, "DELETE FROM dav_cards")
+	_, err := testSvc.db.Exec(ctx, "DELETE FROM dav_cards WHERE uri LIKE 'test-%'")
 	require.NoError(t, err)
 
 	contacts, err := testSvc.ListAllContacts()