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/McRFPy_API.h

@@ -2,6 +2,7 @@
 #include "Common.h"
 #include "Python.h"
 #include <list>
+#include <atomic>
 
 #include "PyFont.h"
 #include "PyTexture.h"
@@ -85,4 +86,10 @@ public:
     static void triggerSceneChange(const std::string& from_scene, const std::string& to_scene);
     static void updatePythonScenes(float dt);
     static void triggerResize(int width, int height);
+
+    // Exception handling - signal game loop to exit on unhandled Python exceptions
+    static std::atomic<bool> exception_occurred;
+    static std::atomic<int> exit_code;
+    static void signalPythonException();  // Called by exception handlers
+    static bool shouldExit();             // Checked by game loop
 };