fix: unified raw room names + merged presence on join

1. CLI client now sends raw room names (no hash), matching Android
   JNI and Desktop Tauri. All three clients are now consistent.

2. When a client joins a global room, the relay merges federated
   remote participants into the initial RoomUpdate. Previously,
   clients that joined after the GlobalRoomActive signal only saw
   local participants. Now they see everyone immediately.

3. Added get_remote_participants() to FederationManager for querying
   cached remote participants from all peer links.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

crates/wzp-relay/src/federation.rs

@@ -241,6 +241,26 @@ impl FederationManager {
         }
     }
 
+    /// Get all remote participants for a room from all peer links.
+    pub async fn get_remote_participants(&self, room: &str) -> Vec<wzp_proto::packet::RoomParticipant> {
+        let canonical = self.resolve_global_room(room);
+        let links = self.peer_links.lock().await;
+        let mut result = Vec::new();
+        for link in links.values() {
+            // Check canonical name
+            if let Some(c) = canonical {
+                if let Some(remote) = link.remote_participants.get(c) {
+                    result.extend(remote.iter().cloned());
+                }
+            }
+            // Also check raw room name
+            if let Some(remote) = link.remote_participants.get(room) {
+                result.extend(remote.iter().cloned());
+            }
+        }
+        result
+    }
+
     /// Forward locally-generated media to all connected peers.
     /// For locally-originated media, we send to ALL peers (they decide whether to deliver).
     /// For forwarded media (multi-hop), handle_datagram filters by active_rooms.