test: add unit tests for valid DConfig configuration

- Add comprehensive test suite for TreelandUserConfig with valid DConfig
- Test immediate destroy, initialization completion, and property changes
- Add stress tests for high-frequency creation/destruction cycles
- Verify safety of signal handling using QPointer mechanism
- Tests confirm crash fix prevents SIGSEGV in production scenarios

Author: Dami-star

tests/CMakeLists.txt

@@ -7,3 +7,4 @@ add_subdirectory(test_protocol_shortcut)
 add_subdirectory(test_protocol_virtual-output)
 add_subdirectory(test_protocol_wallpaper-color)
 add_subdirectory(test_protocol_window-management)
+add_subdirectory(test_treeland_userconfig)

tests/test_treeland_userconfig/CMakeLists.txt

@@ -0,0 +1,15 @@
+set(CMAKE_INCLUDE_CURRENT_DIR ON)
+set(CMAKE_AUTOMOC ON)
+
+# Test with VALID DConfig - reproduces real machine crash (SIGSEGV)
+add_executable(test_dconfig_valid_config test_dconfig_valid_config.cpp)
+target_link_libraries(test_dconfig_valid_config
+    Qt6::Core
+    Qt6::Gui
+    Qt6::Test
+    libtreeland
+)
+target_include_directories(test_dconfig_valid_config PRIVATE
+    ${CMAKE_BINARY_DIR}/src
+)
+add_test(NAME test_dconfig_valid_config COMMAND test_dconfig_valid_config)