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/McRogueFaceConfig.h

@@ -31,6 +31,10 @@ struct McRogueFaceConfig {
 
     // Auto-exit when no timers remain (for --headless --exec automation)
     bool auto_exit_after_exec = false;
+
+    // Exception handling: exit on first Python callback exception (default: true)
+    // Use --continue-after-exceptions to disable
+    bool exit_on_exception = true;
 };
 
 #endif // MCROGUEFACE_CONFIG_H