fix(offline): logout reopens the Qobuz gate; auth endpoints exempt from it

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

crates/qbz-slint/src/auth.rs

@@ -33,6 +33,19 @@ where
 {
     let core = runtime.core();
 
+    // Belt-and-suspenders: signing in is an explicit intent to reach Qobuz.
+    // If a session-scoped offline session is still active (e.g. invoked from
+    // the login screen after a logout that raced the engine reset), end it so
+    // the still-gated parts of the pipeline (cold bundle init, post-login
+    // activation) work. The persisted `induced` preference is NOT touched —
+    // a successful login reloads it via init_for_user and the app correctly
+    // lands back in induced offline.
+    let offline_engine = crate::offline_mode::engine();
+    if offline_engine.status().offline_session {
+        log::info!("[qbz-slint] sign-in requested with an offline session active — ending it");
+        offline_engine.set_offline_session(false);
+    }
+
     // Ensure the Qobuz client is initialized (bundle tokens).
     if !core.is_api_initialized().await {
         core.try_init_api().await.map_err(|e| e.to_string())?;