Fix asymmetric voice/media delivery in private chats

When selectedPrivateChatPeer was migrated to a 64-hex stable Noise key
after session establishment, file transfers would silently fail because:

1. Sender used raw 64-hex key, truncated to first 8 bytes by BinaryProtocol
2. Receiver's myPeerID is SHA256-fingerprint-derived (different value)
3. Recipient check failed, causing silent packet drop

The fix normalizes peerID to short form (SHA256-derived 16-hex) in
sendFilePrivate before constructing recipientData, ensuring the wire
format matches what receivers expect.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

bitchat/Services/BLE/BLEService.swift

@@ -728,7 +728,10 @@ final class BLEService: NSObject {
                 SecureLogger.error("❌ Failed to encode file packet for private send", category: .session)
                 return
             }
-            guard let recipientData = Data(hexString: peerID.id) else {
+            // Normalize to short form (SHA256-derived 16-hex) for wire protocol compatibility
+            // This ensures 64-hex Noise keys are converted to the canonical routing format
+            let targetID = peerID.toShort()
+            guard let recipientData = Data(hexString: targetID.id) else {
                 SecureLogger.error("❌ Invalid recipient peer ID for file transfer: \(peerID)", category: .session)
                 return
             }