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/GameEngine.h

@@ -153,6 +153,7 @@ public:
     std::shared_ptr<Timer> getTimer(const std::string& name);
     void setWindowScale(float);
     bool isHeadless() const { return headless; }
+    const McRogueFaceConfig& getConfig() const { return config; }
     void processEvent(const sf::Event& event);
     
     // Window property accessors