Implement Scene subclass on_key callback support

Scene subclasses can now define on_key(self, key, state) methods that
receive keyboard events, matching the existing on_enter, on_exit, and
update lifecycle callbacks.

Changes:
- Rename call_on_keypress to call_on_key (consistent naming with property)
- Add triggerKeyEvent helper in McRFPy_API
- Call triggerKeyEvent from GameEngine when key_callable is not set
- Fix condition to check key_callable.isNone() (not just pointer existence)
- Handle both bound methods and instance-assigned callables

Usage:
    class GameScene(mcrfpy.Scene):
        def on_key(self, key, state):
            if key == "Escape" and state == "end":
                quit_game()

Property assignment (scene.on_key = callable) still works and takes
precedence when key_callable is set via the property setter.

Includes comprehensive test: tests/unit/scene_subclass_on_key_test.py

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/GameEngine.cpp

@@ -457,11 +457,17 @@ void GameEngine::processEvent(const sf::Event& event)
         std::string name = currentScene()->action(actionCode);
         currentScene()->doAction(name, actionType);
     }
-    else if (currentScene()->key_callable && 
+    else if (currentScene()->key_callable && !currentScene()->key_callable->isNone() &&
              (event.type == sf::Event::KeyPressed || event.type == sf::Event::KeyReleased))
     {
+        // Property-assigned handler (scene.on_key = callable)
         currentScene()->key_callable->call(ActionCode::key_str(event.key.code), actionType);
     }
+    else if (event.type == sf::Event::KeyPressed || event.type == sf::Event::KeyReleased)
+    {
+        // Try subclass on_key method if no property handler is set
+        McRFPy_API::triggerKeyEvent(ActionCode::key_str(event.key.code), actionType);
+    }
 }
 
 void GameEngine::sUserInput()

src/McRFPy_API.h

@@ -80,6 +80,7 @@ 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);
+    static void triggerKeyEvent(const std::string& key, const std::string& action);
 
     // #151: Module-level scene property accessors
     static PyObject* api_get_current_scene();

src/PySceneObject.cpp

@@ -413,23 +413,28 @@ void PySceneClass::call_on_exit(PySceneObject* self)
     }
 }
 
-void PySceneClass::call_on_keypress(PySceneObject* self, std::string key, std::string action)
+void PySceneClass::call_on_key(PySceneObject* self, const std::string& key, const std::string& action)
 {
     PyGILState_STATE gstate = PyGILState_Ensure();
 
-    PyObject* method = PyObject_GetAttrString((PyObject*)self, "on_keypress");
-    if (method && PyCallable_Check(method)) {
-        PyObject* result = PyObject_CallFunction(method, "ss", key.c_str(), action.c_str());
+    // Look for on_key attribute on the Python object
+    // This handles both:
+    // 1. Subclass methods: class MyScene(Scene): def on_key(self, k, s): ...
+    // 2. Instance attributes: ts.on_key = lambda k, s: ...  (when subclass shadows property)
+    PyObject* attr = PyObject_GetAttrString((PyObject*)self, "on_key");
+    if (attr && PyCallable_Check(attr) && attr != Py_None) {
+        // Call it - works for both bound methods and regular callables
+        PyObject* result = PyObject_CallFunction(attr, "ss", key.c_str(), action.c_str());
         if (result) {
             Py_DECREF(result);
         } else {
             PyErr_Print();
         }
-        Py_DECREF(method);
+        Py_DECREF(attr);
     } else {
-        // Clear AttributeError if method doesn't exist
+        // Not callable or is None - nothing to call
         PyErr_Clear();
-        Py_XDECREF(method);
+        Py_XDECREF(attr);
     }
 
     PyGILState_Release(gstate);
@@ -571,6 +576,18 @@ void McRFPy_API::triggerResize(int width, int height)
     }
 }
 
+// Helper function to trigger key events on Python scene subclasses
+void McRFPy_API::triggerKeyEvent(const std::string& key, const std::string& action)
+{
+    GameEngine* game = McRFPy_API::game;
+    if (!game) return;
+
+    // Only notify the active scene if it has an on_key method (subclass)
+    if (python_scenes.count(game->scene) > 0) {
+        PySceneClass::call_on_key(python_scenes[game->scene], key, action);
+    }
+}
+
 // #151: Get the current scene as a Python Scene object
 PyObject* McRFPy_API::api_get_current_scene()
 {

src/PySceneObject.h

@@ -36,7 +36,7 @@ public:
     // Lifecycle callbacks (called from C++)
     static void call_on_enter(PySceneObject* self);
     static void call_on_exit(PySceneObject* self);
-    static void call_on_keypress(PySceneObject* self, std::string key, std::string action);
+    static void call_on_key(PySceneObject* self, const std::string& key, const std::string& action);
     static void call_update(PySceneObject* self, float dt);
     static void call_on_resize(PySceneObject* self, int width, int height);
 
@@ -75,7 +75,7 @@ namespace mcrfpydef {
             "Lifecycle Callbacks (override in subclass):\n"
             "    on_enter(): Called when scene becomes active via activate().\n"
             "    on_exit(): Called when scene is deactivated (another scene activates).\n"
-            "    on_keypress(key: str, action: str): Called for keyboard events. Alternative to on_key property.\n"
+            "    on_key(key: str, action: str): Called for keyboard events (subclass method).\n"
             "    update(dt: float): Called every frame with delta time in seconds.\n"
             "    on_resize(width: int, height: int): Called when window is resized.\n\n"
             "Example:\n"

tests/unit/scene_subclass_on_key_test.py

@@ -0,0 +1,84 @@
+"""Test Scene subclass on_key method callback
+
+Verifies that:
+1. Subclass on_key method is called for keyboard events
+2. Property assignment (scene.on_key = callable) still works
+3. Property assignment on subclass overrides the method
+"""
+import mcrfpy
+from mcrfpy import automation
+import sys
+
+# Test state
+tests_passed = 0
+tests_failed = 0
+
+def test_subclass_method():
+    """Test that subclass on_key method receives keyboard events"""
+    global tests_passed, tests_failed
+    events = []
+
+    class TestScene(mcrfpy.Scene):
+        def on_key(self, key, state):
+            events.append((key, state))
+
+    ts = TestScene('test_method')
+    ts.activate()
+    automation.keyDown('a')
+    automation.keyUp('a')
+
+    if len(events) >= 2:
+        print("PASS: test_subclass_method")
+        tests_passed += 1
+    else:
+        print(f"FAIL: test_subclass_method - got {events}")
+        tests_failed += 1
+
+def test_property_handler():
+    """Test that property assignment works"""
+    global tests_passed, tests_failed
+    events = []
+
+    scene = mcrfpy.Scene('test_property')
+    scene.on_key = lambda k, s: events.append((k, s))
+    scene.activate()
+    automation.keyDown('b')
+    automation.keyUp('b')
+
+    if len(events) >= 2:
+        print("PASS: test_property_handler")
+        tests_passed += 1
+    else:
+        print(f"FAIL: test_property_handler - got {events}")
+        tests_failed += 1
+
+def test_property_overrides_method():
+    """Test that property assignment on subclass overrides the method"""
+    global tests_passed, tests_failed
+    method_events = []
+    property_events = []
+
+    class TestScene(mcrfpy.Scene):
+        def on_key(self, key, state):
+            method_events.append((key, state))
+
+    ts = TestScene('test_override')
+    ts.activate()
+    ts.on_key = lambda k, s: property_events.append((k, s))
+    automation.keyDown('c')
+    automation.keyUp('c')
+
+    if len(property_events) >= 2 and len(method_events) == 0:
+        print("PASS: test_property_overrides_method")
+        tests_passed += 1
+    else:
+        print(f"FAIL: test_property_overrides_method - method={method_events}, property={property_events}")
+        tests_failed += 1
+
+# Run tests
+test_subclass_method()
+test_property_handler()
+test_property_overrides_method()
+
+print(f"\nResults: {tests_passed} passed, {tests_failed} failed")
+sys.exit(0 if tests_failed == 0 else 1)