feat: Exit on first Python callback exception (closes #133)

By default, McRogueFace now exits with code 1 on the first unhandled
exception in timer, click, key, or animation callbacks. This prevents
repeated exception output that wastes resources in AI-driven development.

Changes:
- Add exit_on_exception config flag (default: true)
- Add --continue-after-exceptions CLI flag to preserve old behavior
- Update exception handlers in Timer, PyCallable, and Animation
- Signal game loop via McRFPy_API atomic flags
- Return proper exit code from main()

Before: Timer exceptions repeated 1000+ times until timeout
After: Single traceback, clean exit with code 1

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

src/Timer.cpp

@@ -1,6 +1,8 @@
 #include "Timer.h"
 #include "PythonObjectCache.h"
 #include "PyCallable.h"
+#include "McRFPy_API.h"
+#include "GameEngine.h"
 
 Timer::Timer(PyObject* _target, int _interval, int now, bool _once)
 : callback(std::make_shared<PyCallable>(_target)), interval(_interval), last_ran(now),
@@ -51,10 +53,15 @@ bool Timer::test(int now)
         Py_DECREF(args);
         
         if (!retval)
-        {   
-            std::cout << "Timer callback has raised an exception. It's going to STDERR and being dropped:" << std::endl;
+        {
+            std::cerr << "Timer callback raised an exception:" << std::endl;
             PyErr_Print();
             PyErr_Clear();
+
+            // Check if we should exit on exception
+            if (McRFPy_API::game && McRFPy_API::game->getConfig().exit_on_exception) {
+                McRFPy_API::signalPythonException();
+            }
         } else if (retval != Py_None)
         {   
             std::cout << "Timer returned a non-None value. It's not an error, it's just not being saved or used." << std::endl;