debug(e2ee): add e2ee_state_changed event listener for diagnostics

Log DECRYPTION_FAILED / MISSING_KEY / OK states per participant
to pinpoint exactly what the Rust FFI reports about key setup.

voice.py

@@ -244,6 +244,11 @@ class VoiceSession:
             def on_ts(t, pub, p):
                 logger.info("Track sub: %s %s kind=%s", p.identity, pub.sid, t.kind)
 
+            @self.lk_room.on("e2ee_state_changed")
+            def on_e2ee_state(participant, state):
+                logger.info("E2EE_STATE: participant=%s state=%s(%d)",
+                            participant.identity if participant else "local", state, int(state))
+
             await self.lk_room.connect(self.lk_url, jwt, options=room_opts)
             logger.info("Connected (E2EE=HKDF), remote=%d",
                         len(self.lk_room.remote_participants))