add self updater (#1352)

* add self updater

* remove updater tests after validation

src/updater/UpdateInstaller.h

@@ -0,0 +1,18 @@
+#pragma once
+
+#include <filesystem>
+#include <string>
+
+namespace Kyty::Updater {
+struct Result {
+	bool        success;
+	std::string message;
+};
+
+// Only release files are replaced. Files absent from the release are preserved.
+// Successful installation consumes staged files; stage on the target filesystem.
+Result Validate(const std::filesystem::path& source, const std::filesystem::path& target,
+                const std::filesystem::path& launcher_relative);
+Result Install(const std::filesystem::path& source, const std::filesystem::path& target,
+               const std::filesystem::path& launcher_relative);
+} // namespace Kyty::Updater