Schema: add running_balance column to vault table

functions.php

@@ -34,7 +34,8 @@ function getDatabaseConnection() {
         user            TEXT NOT NULL,
         timestamp       INTEGER NOT NULL,
         description     TEXT NOT NULL,
-        amount REAL NOT NULL
+        amount          REAL NOT NULL,
+        running_balance INTEGER
     );";
 
     if ($pdo === null) {
@@ -43,6 +44,13 @@ function getDatabaseConnection() {
             $pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
 
             $pdo->exec($createTableSQL);
+
+            // Add the running_balance column for databases created before the
+            // column was added. Idempotent: skip if it already exists.
+            $columns = $pdo->query("PRAGMA table_info(vault)")->fetchAll(PDO::FETCH_COLUMN, 1);
+            if (!in_array('running_balance', $columns, true)) {
+                $pdo->exec('ALTER TABLE vault ADD COLUMN running_balance INTEGER');
+            }
         } catch (PDOException $e) {
             die("Database connection failed: " . $e->getMessage());
         }