Perf(license): mutex + write-suppression for licenses.ini hot path

licenses.ini was hit on every heartbeat -- 5s x clients x ~8 SetStr per
auth -- with no concurrency protection. Two consequences:
  1. 100 concurrent online would saturate the file (~160 writes/sec,
     full-file rewrite each via WritePrivateProfileString).
  2. Concurrent SetPendingRenewal / DecrementPendingQuota with no lock
     occasionally clobbered freshly-set renewal quotas (reported by
     user as "preset renewal silently disappears").

Add LicensesIniMutex() (Meyers singleton recursive_mutex, exposed in
CPasswordDlg.h so both CPasswordDlg.cpp and CLicenseDlg.cpp share it)
and wrap all 15 functions that touch licenses.ini.

Rewrite UpdateLicenseActivity around g_activityCache (in-memory state
keyed by "SN|IP|machine"): skip the entire write path when nothing
changed and the 30s LastActiveTime throttle window hasn't expired.
Passcode/HMAC are only flushed on actual change (renewal path); IP
list is only rewritten when the yyMMdd timestamp would roll a day.

Measured impact (local 2-client baseline):
  before: 0.60 writes/sec (4 writes per heartbeat cluster)
  after:  0.07 writes/sec (one write per client per 30s throttle)

Extrapolated to the 100-online target:
  before: ~160 writes/sec (saturation)
  after:  ~3.3 writes/sec  (100 clients / 30s throttle window)

Race elimination is the more important win: PendingQuota's
read-modify-write is now atomic, so the "preset renewal disappears"
race is closed.

Notes from audit (these landed during the same iteration):
- Cache key is (SN, IP, machine), not SN alone. A single SN can be
  shared by 100+ end machines in bulk-license deployments, so a
  per-SN cache flips on every heartbeat and defeats suppression.
  Per-(SN, IP, machine) throttling is what makes the 100/30 model
  actually hold; an SN-only key reproduced the original ~0.7 writes/s.
- DeleteLicense invalidates the per-SN activity cache via
  InvalidateLicenseActivityCache() (prefix scan since one SN maps to
  many cache entries). Without this, cache hits after delete would
  skip the auto-recreate path and leave the section permanently
  missing.
- OnLicenseViewIPs: m_ListLicense.SetItemText moved outside the lock
  so the critical section only covers disk I/O.

server/2015Remote/CPasswordDlg.h

@@ -2,10 +2,23 @@
 
 #include <afx.h>
 #include <afxwin.h>
+#include <mutex>
 #include "Resource.h"
 #include "common/commands.h"
 #include "LangManager.h"
 
+// 全局 licenses.ini 互斥锁（Meyers singleton，跨翻译单元共享）。
+// 所有读写 licenses.ini 的函数入口必须加锁，否则在心跳并发下会出现
+// read-modify-write 丢更新（典型受害者：PendingQuota / IP 列表）。
+// 使用 recursive_mutex 是因为部分函数会嵌套调用（如 DecrementPendingQuota → ClearPendingRenewal）。
+std::recursive_mutex& LicensesIniMutex();
+
+// 让 UpdateLicenseActivity 内部缓存里某个 SN 的 entry 失效。
+// 必须在外部修改了授权（删除 / 重新创建 section）后调用，否则 cache 命中策略
+// 会跳过本应触发的"既往授权自动加入"路径，导致 disk 上的 section 不会重建。
+// 实现在 CPasswordDlg.cpp，需持 LicensesIniMutex（内部会自行加锁，可在已加锁线程嵌套调用）。
+void InvalidateLicenseActivityCache(const std::string& deviceID);
+
 // CPasswordDlg 对话框
 namespace TcpClient {
     std::string ObfuscateAuthorization(const std::string& auth);