Implement proper room leave notifications and improve UI

- Send leave notifications when users exit rooms
- Update room member lists when peers leave rooms
- Change current user icon from dot to person.fill
- Handle room-specific leave messages via protocol
- Maintain backwards compatibility for general peer disconnection

bitchat/Protocols/BitchatProtocol.swift

@@ -155,6 +155,7 @@ protocol BitchatDelegate: AnyObject {
     func didConnectToPeer(_ peerID: String)
     func didDisconnectFromPeer(_ peerID: String)
     func didUpdatePeerList(_ peers: [String])
+    func didReceiveRoomLeave(_ room: String, from peerID: String)
     
     // Optional method to check if a fingerprint belongs to a favorite peer
     func isFavorite(fingerprint: String) -> Bool
@@ -165,4 +166,8 @@ extension BitchatDelegate {
     func isFavorite(fingerprint: String) -> Bool {
         return false
     }
+    
+    func didReceiveRoomLeave(_ room: String, from peerID: String) {
+        // Default empty implementation
+    }
 }