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

scripts/managers/goal_manager.gd

@@ -62,8 +62,6 @@ func mark_goal_complete(player_id: int):
 	player_completion_times[player_id].append(duration_sec)
 	# Reset start time for next goal
 	player_start_times[player_id] = Time.get_ticks_msec()
-	
-	# print("Player %s completed goal in %.2fs" % [player_id, duration_sec])
 
 func get_player_average_time(player_id: int) -> float:
 	if not player_completion_times.has(player_id) or player_completion_times[player_id].is_empty():
@@ -92,7 +90,7 @@ func get_boost_multiplier(player_id: int) -> float:
 	var p_avg = get_player_average_time(player_id)
 	var g_avg = get_global_average_time()
 	
-	if p_avg > g_avg: 
+	if p_avg > g_avg:
 		# Player is slower than average -> Boost fills faster
 		# Scale up to 1.5x based on how much slower (capped)
 		var ratio = p_avg / max(g_avg, 0.1)