SignOutService class Providers

The one way to sign out of DuTaTo. Every sign-out control (navigation drawer, Settings → Account, the MFA prompt, account deletion, the forced password update) calls signOut; nothing else calls auth.signOut() (test/presentation/providers/sign_out_provider_test.dart enforces it).

It first removes this device's push token from device_tokens, so a signed-out phone stops receiving the previous account's reminders. That has to happen while the session still exists: the row is only deletable by its owner under RLS. On web, and on a native build without Firebase, that step is a no-op or fails; either way it is logged and never blocks the sign-out itself. It is also given only a few seconds: on a stalled or captive network the token lookup or the delete can hang, and the user would see "Sign out" do nothing.

What must be cleared after sign-out (AI credentials, cached user data) hangs off the signedOut auth event in main.dart instead, so it also runs when the session ends for any other reason.