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_spinlock.cpp

@@ -0,0 +1,32 @@
+#include <gtest/gtest.h>
+#include <XCEngine/Threading/SpinLock.h>
+
+using namespace XCEngine::Threading;
+
+namespace {
+
+TEST(Threading_SpinLock, LockUnlock) {
+    SpinLock spinlock;
+    
+    spinlock.Lock();
+    spinlock.Unlock();
+}
+
+TEST(Threading_SpinLock, TryLock_Success) {
+    SpinLock spinlock;
+    
+    bool result = spinlock.TryLock();
+    EXPECT_TRUE(result);
+    spinlock.Unlock();
+}
+
+TEST(Threading_SpinLock, TryLock_AlreadyLocked) {
+    SpinLock spinlock;
+    
+    spinlock.Lock();
+    bool result = spinlock.TryLock();
+    EXPECT_FALSE(result);
+    spinlock.Unlock();
+}
+
+} // namespace