feat: add rigged+animated Miku player model with auto-rig pipeline

- Add miku_rigged_animated.glb (3.27MB) with 18-bone skeleton and 6 animations
  (Idle, Walk, Run, Jump, Crouch, Death) via Blender auto-rig script
- Add tools/rig_and_animate.py: reusable Blender script for rigging any humanoid
  mesh with Mixamo-compatible bone naming
- Update SkinnedPlayerModel: scale_factor, first-person mode, animation state
  matching (Idle/Walk/Run/Jump/Crouch/Death)
- Update level_runtime.gd: use skinned model for local player, procedural
  humanoid for remote players
- Update skin_manager.gd and test_level_builder.gd to use animated model
- Fix Godot 4.2.1 'is not Type' syntax in 5 weapon files
- Add editor/import_miku_to_tscn.gd for editor-based GLB import

weapons/explosive_projectile.gd

@@ -193,7 +193,7 @@ func _explode(pos: Vector3) -> void:
 		
 		# Apply knockback if it has server_apply_impulse (for rocket jumping)
 		if col.has_method("server_apply_impulse") and col == owner_player:
-			if multiplayer.has_multiplayer_peer() and multiplayer.multiplayer_peer is not OfflineMultiplayerPeer:
+			if multiplayer.has_multiplayer_peer() and not(multiplayer.multiplayer_peer is OfflineMultiplayerPeer):
 				col.server_apply_impulse.rpc_id(1, dir * final_knockback)
 			else:
 				col.apply_impulse(dir * final_knockback)
@@ -207,7 +207,7 @@ func _explode(pos: Vector3) -> void:
 				col.take_damage(final_damage, target_pos, owner_player, dir * final_knockback)
 				
 	# Broadcast Visual Explosion Effect to other peers
-	if owner_player and owner_player.is_multiplayer_authority() and owner_player.has_method("server_play_explosion") and owner_player.multiplayer.has_multiplayer_peer() and owner_player.multiplayer.multiplayer_peer is not OfflineMultiplayerPeer:
+	if owner_player and owner_player.is_multiplayer_authority() and owner_player.has_method("server_play_explosion") and owner_player.multiplayer.has_multiplayer_peer() and not(owner_player.multiplayer.multiplayer_peer is OfflineMultiplayerPeer):
 		owner_player.server_play_explosion.rpc_id(1, pos, explosion_radius)
 		
 	# Local Visual Effect