fix: allow reconnect while auth listener is still active

[LurigeLars]

After a confirmed disconnect, the local listener is intentionally kept alive briefly so the confirmation page can finish rendering. If connect_avanza is called during that grace period, open_browser() reuses the existing listener but previously left the auth state as disconnected.

That meant the browser could reopen, but /start would not begin a new BankID authentication because approval is only accepted while the state is awaiting_approval.

This change:

• resets retryable terminal states to awaiting_approval when an existing listener is reused
• clears any stale auth error code
• adds a regression test covering:
  connected -> confirmed disconnect -> immediate reconnect -> new BankID start

The production change is limited to three lines and does not change session storage, credential handling, or the normal disconnect flow.