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>

tests/notes/test_exception_exit.py

@@ -0,0 +1,31 @@
+#!/usr/bin/env python3
+"""Test for --continue-after-exceptions behavior (Issue #133)
+
+This test verifies that:
+1. By default, unhandled exceptions in timer callbacks cause immediate exit with code 1
+2. With --continue-after-exceptions, exceptions are logged but execution continues
+"""
+
+import mcrfpy
+import sys
+
+def timer_that_raises(runtime):
+    """A timer callback that raises an exception"""
+    raise ValueError("Intentional test exception")
+
+# Create a test scene
+mcrfpy.createScene("test")
+mcrfpy.setScene("test")
+
+# Schedule the timer - it will fire after 50ms
+mcrfpy.setTimer("raise_exception", timer_that_raises, 50)
+
+# This test expects:
+# - Default behavior: exit with code 1 after first exception
+# - With --continue-after-exceptions: continue running (would need timeout or explicit exit)
+#
+# The test runner should:
+# 1. Run without --continue-after-exceptions and expect exit code 1
+# 2. Run with --continue-after-exceptions and expect it to not exit immediately
+
+print("Test initialized - timer will raise exception in 50ms")