fix: retry OpenClipboard() on Windows

OpenClipboard() can fail transiently when another process holds the
clipboard mutex. Add a retry loop (5 attempts, 5ms delay) so that
Deskflow handles brief contention gracefully instead of immediately
failing.

src/lib/platform/MSWindowsClipboard.cpp

@@ -1,5 +1,6 @@
 /*
  * Deskflow -- mouse and keyboard sharing utility
+ * SPDX-FileCopyrightText: (C) 2026 Deskflow Developers
  * SPDX-FileCopyrightText: (C) 2012 - 2016 Symless Ltd.
  * SPDX-FileCopyrightText: (C) 2002 Chris Schoeneman
  * SPDX-License-Identifier: GPL-2.0-only WITH LicenseRef-OpenSSL-Exception
@@ -116,14 +117,26 @@ bool MSWindowsClipboard::open(Time time) const
 {
   LOG_DEBUG("open clipboard");
 
-  if (!OpenClipboard(m_window)) {
-    LOG_WARN("failed to open clipboard: %d", GetLastError());
-    return false;
+  // The clipboard is a global mutex on Windows. We aren't always going to
+  // get the lock on the first try, so try a few times before giving up.
+  // Based on Chromium's ScopedClipboard::Acquire() retry loop.
+  static const int kMaxRetries = 5;
+  static const int kRetryDelayMs = 5;
+
+  for (int i = 0; i < kMaxRetries; ++i) {
+    if (OpenClipboard(m_window)) {
+      m_time = time;
+      return true;
+    }
+
+    if (i < kMaxRetries - 1) {
+      LOG_DEBUG("failed to open clipboard (attempt %d/%d, error=%d), retrying", i + 1, kMaxRetries, GetLastError());
+      Sleep(kRetryDelayMs);
+    }
   }
 
-  m_time = time;
-
-  return true;
+  LOG_WARN("failed to open clipboard after %d attempts: %d", kMaxRetries, GetLastError());
+  return false;
 }
 
 void MSWindowsClipboard::close() const