Add Ctrl+Return cheat to instantly win the current level

During gameplay, pressing Ctrl+Return triggers an immediate level clear:
the current level is marked as won (level_clear, or run_complete on the
last DAT level) and the state transitions to VICTORY, showing the
normal 'Level Clear!' dialog so the player can then advance with Return.

Implementation:
- engine/sdl2.py: mainloop detects Ctrl+Return via SDLK_RETURN + KMOD_CTRL
  and dispatches a 'cheat_win_level' action (bypassing keybindings).
- engine/controls.py: trigger() now also accepts direct action names that
  are registered in the dispatcher (not key-event names), and a new
  cheat_win_level handler forwards to the game.
- rats.py: MiceMaze.cheat_win_level() performs the win, guarded so it only
  fires while a level is actively being played.

No keybinding files need editing; the cheat is wired through the engine
layer directly.

engine/controls.py

@@ -211,6 +211,7 @@ class KeyBindings:
             "toggle_pause": self.toggle_pause,
             "toggle_full_screen": self.toggle_full_screen,
             "quit_game": self.quit_game,
+            "cheat_win_level": self.cheat_win_level,
             "menu_up": self.game.menu_up,
             "menu_down": self.game.menu_down,
             "menu_left": self.game.menu_left,
@@ -298,6 +299,17 @@ class KeyBindings:
         if not self.bindings:
             self.initialize_keybindings()
 
+        # Direct action dispatch: if the action name itself is a registered
+        # dispatcher entry (e.g. cheat actions injected by the engine layer),
+        # invoke it without requiring a keybinding entry.
+        direct_method = self.action_dispatcher.get(action)
+        if direct_method is not None and action not in ("spawn_rat",):
+            # Only treat as direct when the action isn't also a normal key event
+            # name. Key events look like "keydown_*" / "keyup_*" / etc.
+            if not action.startswith(("keydown_", "keyup_", "joybutton", "joyhat", "controller", "mousemove")):
+                direct_method()
+                return None
+
         value = None
         for section_name in self._binding_sections_for_action():
             value = self.bindings.get(section_name, {}).get(action)
@@ -319,6 +331,11 @@ class KeyBindings:
             method()
         return None
 
+    def cheat_win_level(self):
+        """Cheat handler: win the current level instantly (Ctrl+Return)."""
+        if hasattr(self.game, "cheat_win_level"):
+            self.game.cheat_win_level()
+
     def spawn_rat(self):
         self.game.unit_manager.spawn_rat()