refactor: add window::stop() and remove quit flag

Added `window::stop()` (sets GLFW close flag). Updated
signal/timer handlers and Q key check to call it instead of
using a separate `quit` bool in main().

This encapsulates the close state in the window class (no
more external flag + manual checks). The render loop is now
simpler.

(The process_signals lambda and ASIO duration timer are
retained.)

cuber.cpp

@@ -50,10 +50,9 @@ auto main(int argc, char const* argv[]) -> int {
     // signal handling + optional duration timer (via ASIO)
     asio::io_context io;
     asio::signal_set signals(io, SIGINT, SIGTERM);
-    bool quit = false;
 
     signals.async_wait([&](auto, auto) {
-        quit = true;
+        win.stop();
         io.stop();
     });
 
@@ -61,9 +60,9 @@ auto main(int argc, char const* argv[]) -> int {
     if (max_duration_seconds > 0.0f) {
         duration_timer.expires_after(std::chrono::milliseconds(
             static_cast<long long>(max_duration_seconds * 1000.0f)));
-        duration_timer.async_wait([&](auto ec) {
+        duration_timer.async_wait([&win](auto ec) {
             if (!ec) {
-                quit = true;
+                win.stop();
             }
         });
     }
@@ -78,11 +77,11 @@ auto main(int argc, char const* argv[]) -> int {
     while (!win.should_close()) {
         process_signals();
 
-        auto now = std::chrono::steady_clock::now();
-        if (quit || glfwGetKey(win.raw(), GLFW_KEY_Q) == GLFW_PRESS) {
-            break;
+        if (glfwGetKey(win.raw(), GLFW_KEY_Q) == GLFW_PRESS) {
+            win.stop();
         }
 
+        auto now = std::chrono::steady_clock::now();
         auto dt = std::chrono::duration<float>(now - prev).count();
         prev = now;