Logging out of an offline session left offline_session set and the gate
closed, refusing the very OAuth exchange that could end the offline state
(user-reproduced: sign-in failed with OfflineMode after logout). teardown()
now ends the session-scoped offline state (offline_session and the cached
induced flag reset; the persisted preference reloads on the next
activation) and recomputes, reopening the gate when connectivity allows.
Two regression tests added.
The three login methods (login, login_with_oauth_code, login_with_token)
are exempt from the offline gate: user-initiated sign-in is explicit
intent to reach Qobuz; the gate governs services. Verified none of them
reach gated sub-calls; bundle cold-start stays gated on purpose. New unit
test pins the exemption. The recovery sign-in falls back to the full
browser OAuth flow when the saved token is gone or rejected, and
offline_session is lifted only on success paths.
cc