experimental: remove Tekton Doors entirely

- Delete portal_mode_manager.gd, portal_door.gd, portal_door.tscn
- Strip all Tekton Doors logic from main.gd, player.gd, lobby.gd,
  lobby_room.gd, lobby_manager.gd, camera_context_manager.gd,
  music_manager.gd, tekton.gd, enhanced_gridmap.gd,
  playerboard_manager.gd, special_tiles_manager.gd
- Remove TK enum (TEKTON_DOORS=2), mode_config schema, arena area
- Update tests: 3 modes instead of 4
- Strip HowToPlay tab from main.tscn

scenes/player.gd

@@ -1767,14 +1767,7 @@ func start_movement_along_path(path: Array, clear_visual: bool = true, force: bo
 				if sng_manager and sng_manager.has_method("check_win_condition"):
 					if sng_manager.check_win_condition(name.to_int(), current_position):
 						sng_main.rpc("sync_game_end_stop_n_go", name.to_int())
-		
-		# Tekton Doors Win Check
-		elif LobbyManager.game_mode == "Tekton Doors":
-			var main_node = get_tree().root.get_node_or_null("Main")
-			if main_node and main_node.portal_mode_manager:
-				if main_node.portal_mode_manager.check_win_condition(name.to_int(), current_position):
-					main_node.rpc("sync_game_end_portal_mode", name.to_int())
-		
+
 		# FORCE SNAP: Update target visual position to the perfect grid center
 		# This ensures that when interpolation resumes (in _process), it pulls to the correct spot
 		target_visual_position = grid_to_world(current_position)