fix(voice): log remote participant identity and track count in E2EE poll

Adds REMOTE_PARTICIPANT log every 10s to confirm caller is present
and tracks are subscribed during E2EE decryption diagnosis.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

voice.py

@@ -375,6 +375,10 @@ class VoiceSession:
                                         c.participant_identity, c.key_index, c.enabled)
                     except Exception as e:
                         logger.debug("frame_cryptors() failed: %s", e)
+                    # Log E2EE state for all remote participants
+                    for p in self.lk_room.remote_participants.values():
+                        logger.info("REMOTE_PARTICIPANT: identity=%s tracks=%d",
+                                    p.identity, len(p.track_publications))
 
         except asyncio.CancelledError:
             logger.info("Session cancelled for %s", self.room_id)