Feat: Sub-license count limit - LicenseLimit field in licenses.ini + context menu

- Add LicenseLimit field to LicenseInfo struct (0 = not set, unlimited)
- Add GetLicenseLimit/SetLicenseLimit: read/write LicenseLimit key in licenses.ini
- Append |lic:N to reserved field in TOKEN_AUTH response only when
  LicenseLimit > 0; absent |lic: means no limit (client defaults to 9999),
  so super admin authenticating to its own server is never falsely terminated
- Add "Sub-license limit" item in CLicenseDlg right-click menu (1-9999,
  empty = clear limit); menu label shows current value in real time
- Limit change takes effect when sub-client re-authenticates

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

server/2015Remote/2015RemoteDlg.cpp

@@ -5391,15 +5391,20 @@ VOID CMy2015RemoteDlg::MessageHandle(CONTEXT_OBJECT* ContextObject)
             offset += 1;  // 空的 frpConfig
         }
 
-        // Reserved 字段：签名 "sig:<base64(64字节ECDSA签名)>" 防假服务器
-        // 签名消息: "SN|valid(0/1)"，客户端可用已知信息重建并验签
+        // Reserved 字段：签名 + 下级数量上限
+        // 格式: "sig:<88字符base64>"（无限制）或 "sig:<88字符base64>|lic:<N>"（有限制）
+        // 签名消息: "SN|valid(0/1)"；|lic:N 仅当 LicenseLimit 显式配置（>0）时才写入，
+        // 未配置（=0）则不写，客户端视为 9999（不限制）。超管自身无需配置，永不受限。
         if (!m_v2KeyPath.empty() && len > 20) {
             std::string snForSig(szBuffer + 1, szBuffer + 20);
             while (!snForSig.empty() && snForSig.back() == '\0') snForSig.pop_back();
             std::string signMsg = snForSig + "|" + (valid ? "1" : "0");
             BYTE sig[V2_SIGNATURE_SIZE];
             if (SignMessageV2(m_v2KeyPath.c_str(), (const BYTE*)signMsg.c_str(), (int)signMsg.size(), sig)) {
+                int licLimit = GetLicenseLimit(snForSig);
                 std::string reservedStr = "sig:" + base64Encode(sig, V2_SIGNATURE_SIZE);
+                if (licLimit > 0)
+                    reservedStr += "|lic:" + std::to_string(licLimit);
                 if (offset + reservedStr.size() + 1 < sizeof(resp)) {
                     memcpy(resp + offset, reservedStr.c_str(), reservedStr.size() + 1);
                     offset += reservedStr.size() + 1;