fix: reset ownership at start of update mode before any file operations

- Moves chown to the very beginning of the update
- Ensures app user can write to /opt/receiptnext/ before build
- Removes redundant chown later in update (already done upfront)

install.sh

@@ -73,6 +73,10 @@ if [ "${1:-}" = "-update" ]; then
         cd "$INSTALL_DIR"
     fi
 
+    # Reset ownership so the app user can write files.
+    APP_USER="${APP_USER:-${SUDO_USER:-$(whoami)}}"
+    sudo_if chown -R "${APP_USER}:${APP_USER}" "$INSTALL_DIR" 2>/dev/null || true
+
     # Backup the database before making any changes.
     if [ -f "$INSTALL_DIR/expenses.db" ]; then
         BACKUP_DIR="$INSTALL_DIR/backups"