chore: init frontend+backend skeleton

backend/tests/test_main.cc

@@ -0,0 +1 @@
+// Intentionally empty: Catch2WithMain provides main().

backend/tests/version_test.cc

@@ -0,0 +1,8 @@
+#include <catch2/catch_test_macros.hpp>
+
+#include "csp/version.h"
+
+TEST_CASE("version is non-empty") {
+  REQUIRE(csp::kVersion != nullptr);
+  REQUIRE(std::string(csp::kVersion).size() > 0);
+}