Fix peer nickname display once and for all

- Only show peers in UI who have announced (have nicknames)
- Filter out peers without nicknames from getAllConnectedPeerIDs()
- Send announces proactively when app starts, not just on connection
- Send announces immediately when nickname changes via saveNickname()
- Send announces when Bluetooth services become available
- Send announces multiple times (0.5s, 1s, 2s) for reliability
- Add sendBroadcastAnnounce() method for proactive announcing

This ensures peers always see proper nicknames, never 'person-xxx'

bitchat/ViewModels/ChatViewModel.swift

@@ -61,6 +61,9 @@ class ChatViewModel: ObservableObject {
     func saveNickname() {
         userDefaults.set(nickname, forKey: nicknameKey)
         userDefaults.synchronize() // Force immediate save
+        
+        // Send announce with new nickname to all peers
+        meshService.sendBroadcastAnnounce()
     }
     
     private func loadFavorites() {