feat: implement stopwatch timer

Replace Hello World with a live stopwatch that prints elapsed time
in HH:MM:SS.mmm format, updating every 10ms with color output.

cuber.cpp

@@ -1,6 +1,27 @@
-#include <fmt/core.h>
-
-auto main(int argc, char const* argv[]) -> int {
-    fmt::print("Hello, World!\n");
-    return 0;
-}
+#include <chrono>
+#include <thread>
+
+#include "fmt/std.h"
+
+auto main(int argc, char const* argv[]) -> int {
+    using namespace std::chrono;
+    using namespace std::literals;
+
+    auto start = steady_clock::now();
+
+    while (true) {
+        auto elapsed = steady_clock::now() - start;
+        auto totalSec = duration_cast<seconds>(elapsed).count();
+        auto h = totalSec / 3600;
+        auto m = (totalSec % 3600) / 60;
+        auto s = totalSec % 60;
+        auto ms = duration_cast<milliseconds>(elapsed % 1s).count();
+
+        fmt::print("\033[32m{:02}:{:02}:{:02}\033[0m.\033[90m{:03}\033[0m\r",
+                   h, m, s, ms);
+
+        std::this_thread::sleep_for(10ms);
+    }
+
+    return 0;
+}