chore: snapshot editor work and restore tests

Key points:\n- restore the tests tree removed by bc47e6e\n- capture current editor workspace, scene, and docs reshuffle changes\n- keep local cloud.nvdb resources ignored from this commit

tests/threading/test_mutex.cpp

@@ -0,0 +1,41 @@
+#include <gtest/gtest.h>
+#include <XCEngine/Threading/Mutex.h>
+
+using namespace XCEngine::Threading;
+
+namespace {
+
+TEST(Threading_Mutex, LockUnlock) {
+    Mutex mutex;
+    
+    mutex.Lock();
+    mutex.Unlock();
+}
+
+TEST(Threading_Mutex, TryLock_Success) {
+    Mutex mutex;
+    
+    bool result = mutex.TryLock();
+    EXPECT_TRUE(result);
+    mutex.Unlock();
+}
+
+TEST(Threading_Mutex, TryLock_AlreadyLocked) {
+    Mutex mutex;
+    
+    mutex.Lock();
+    bool result = mutex.TryLock();
+    EXPECT_FALSE(result);
+    mutex.Unlock();
+}
+
+TEST(Threading_Mutex, MultipleLockUnlock) {
+    Mutex mutex;
+    
+    for (int i = 0; i < 10; ++i) {
+        mutex.Lock();
+        mutex.Unlock();
+    }
+}
+
+} // namespace