Feature: sub-connection auth (TOKEN_CONN_AUTH) with HMAC + clientID binding

Client first packet on every sub-connection signs (clientID || timestamp ||
nonce) and waits for server ack. Server verifies signature and pins clientID
on the sub-connection ctx, eliminating IP-reverse-lookup unreliability for
NAT/localhost scenarios. Sub-conn coverage: Win 12 sites, Linux/macOS 3-4
each. Main connection keeps existing TOKEN_LOGIN flow unchanged.

Includes:
- Protocol structs sized to 512/256 bytes with reserved space for future
  extensions (locale, OS info, session token, etc.)
- 5-min timestamp tolerance (Kerberos-grade replay window)
- 10-sec client wait for cross-pacific / weak-network tolerance
- Fix RemoveFromHostList side-effect ordering: MarkDeviceOffline and
  m_ActiveWndW.erase now only fire when ctx is actually removed from
  m_HostList, preventing sub-conn disconnects from misreporting main as
  offline (regression introduced by auth-set clientID on sub ctx)
- Fix latent bug: IOCPClient::m_conn was never assigned in ctor, leaving
  GetConnectionAddress() always NULL and FileManager V2 transfer's
  srcClientID always 0

Breaking change: new client cannot use sub-features against old server.
New server tolerates legacy clients (no auth). Future tightening can reject
unauthenticated sub-connections via IsAuthenticated() flag.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

client/FileManager.cpp

@@ -1163,6 +1163,7 @@ void CFileManager::UploadToRemoteV2(LPBYTE lpBuffer, UINT nSize)
 
     // 创建新连接发送文件
     IOCPClient* pClient = new IOCPClient(g_bExit, true, MaskTypeNone, conn);
+    pClient->EnableSubConnAuth();   // V2 文件传输子连接：每次连上后自动发 TOKEN_CONN_AUTH 校验
     if (pClient->ConnectServer(m_ClientObject->ServerIP().c_str(), m_ClientObject->ServerPort())) {
         std::thread([allFiles, targetDir = std::string(targetDir), pClient, opts, hash, hmac]() {
             FileBatchTransferWorkerV2(allFiles, targetDir, pClient,