refactored export functionality

db_init.php

@@ -78,6 +78,12 @@ function qdb_open(bool $writable = false): array {
         }
         $pdo->exec("PRAGMA user_version = " . QDB_VERSION . ";");
         $pdo->exec("PRAGMA foreign_keys = ON;");
+
+        // Persist upgrade even when opened read-only (otherwise migration is lost on discard)
+        if (!$writable) {
+            qdb_save($tmpDb, $lockFp);
+            return qdb_open(false);
+        }
     }
 
     return [$pdo, $tmpDb, $lockFp];