feat: add ASIO signal handling for graceful shutdown

- Add asio dependency for async signal handling
- Register SIGINT and SIGTERM to quit the application
- Poll signals each frame for non-blocking shutdown
- Q key and Ctrl+C both cleanly exit the program

cuber.cpp

@@ -3,6 +3,10 @@
 
 #include "cbt/window.hpp"
 
+#include <csignal>
+
+#include <asio.hpp>
+
 #include "glad/glad.h"
 
 auto main(int, char const*[]) -> int {
@@ -12,8 +16,23 @@ auto main(int, char const*[]) -> int {
         return 1;
     }
 
+    asio::io_context io;
+    asio::signal_set signals(io, SIGINT, SIGTERM);
+    bool quit = false;
+
+    signals.async_wait([&](auto, auto) {
+        quit = true;
+        io.stop();
+    });
+
+    auto process_signals = [&]() -> void {
+        while (io.poll()) {}
+    };
+
     while (!w.should_close()) {
-        if (glfwGetKey(static_cast<GLFWwindow*>(w.raw()), GLFW_KEY_Q) == GLFW_PRESS) {
+        process_signals();
+
+        if (quit || glfwGetKey(static_cast<GLFWwindow*>(w.raw()), GLFW_KEY_Q) == GLFW_PRESS) {
             break;
         }