fix: address 7 code review findings for V2 architecture

HIGH priority fixes:
- Enable WAL mode in qbz-integrations caches (ADR-002)
- v2_auto_login/v2_manual_login now call activate_session()
- RequiresUserSession allows offline sessions (only checks session_activated)

MEDIUM priority fixes:
- Consolidate lifecycle: legacy commands delegate to session_lifecycle
- ListenBrainz teardown now calls disconnect() to clear tokens
- Add SessionActivationFailed degraded reason and emit event on failure

crates/qbz-integrations/src/listenbrainz/cache.rs

@@ -21,6 +21,10 @@ impl ListenBrainzCache {
         let conn = Connection::open(db_path)
             .map_err(|e| format!("Failed to open ListenBrainz cache: {}", e))?;
 
+        // Enable WAL mode for concurrent read/write (ADR-002)
+        conn.execute_batch("PRAGMA journal_mode=WAL; PRAGMA synchronous=NORMAL;")
+            .map_err(|e| format!("Failed to enable WAL mode: {}", e))?;
+
         let cache = Self { conn };
         cache.init_schema()?;
 

crates/qbz-integrations/src/musicbrainz/cache.rs

@@ -31,6 +31,10 @@ impl MusicBrainzCache {
         let conn = Connection::open(db_path)
             .map_err(|e| format!("Failed to open MusicBrainz cache: {}", e))?;
 
+        // Enable WAL mode for concurrent read/write (ADR-002)
+        conn.execute_batch("PRAGMA journal_mode=WAL; PRAGMA synchronous=NORMAL;")
+            .map_err(|e| format!("Failed to enable WAL mode: {}", e))?;
+
         let cache = Self { conn };
         cache.init_schema()?;