Fix Noise session persistence during peer ID rotation

- Add session migration when peer IDs rotate
- Sessions now follow peers across ID changes via fingerprint
- Add migratePeerSession to NoiseEncryptionService
- Add migrateSession to NoiseSessionManager
- Integrate migration in BluetoothMeshService updatePeerBinding

This fixes the issue where established Noise sessions were lost
when peer IDs rotated, causing "No Noise session" errors and
requiring re-handshake.

bitchat/Noise/NoiseSession.swift

@@ -259,6 +259,19 @@ class NoiseSessionManager {
         }
     }
     
+    func migrateSession(from oldPeerID: String, to newPeerID: String) {
+        _ = managerQueue.sync(flags: .barrier) {
+            // Check if we have a session for the old peer ID
+            if let session = sessions[oldPeerID] {
+                // Move the session to the new peer ID
+                sessions[newPeerID] = session
+                sessions.removeValue(forKey: oldPeerID)
+                
+                SecurityLogger.log("Migrated Noise session from \(oldPeerID) to \(newPeerID)", category: SecurityLogger.noise, level: .info)
+            }
+        }
+    }
+    
     func getEstablishedSessions() -> [String: NoiseSession] {
         return managerQueue.sync {
             return sessions.filter { $0.value.isEstablished() }