feat(multiplayer): ENet networking + player/world sync + lobby menu + chat

Add dedicated server / host / client modes via NetworkManager autoload,
PlayerSyncComponent (20 Hz unreliable RPC), WorldSyncComponent (authoritative
block break/place), ChatManager (F2), LobbyMenu scene, updated MainMenu
with Solo/Heberger/Rejoindre/Quitter buttons. Port changed to 7777
(9999 occupied by sntlkeyssrvr on this machine). Mobs disabled in multi
(spawn solo only). Solo mode untouched.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

scripts/net/NetworkManager.gd

@@ -0,0 +1,132 @@
+extends Node
+
+signal connection_succeeded()
+signal connection_failed()
+signal server_started()
+signal server_closed()
+signal peer_connected(id: int)
+signal peer_disconnected(id: int)
+
+enum Mode { NONE, SOLO, HOST, CLIENT, DEDICATED }
+var current_mode: Mode = Mode.NONE
+
+const DEFAULT_PORT := 7777
+const MAX_PLAYERS := 16
+
+var peer: ENetMultiplayerPeer = null
+
+
+func _ready() -> void:
+	multiplayer.peer_connected.connect(_on_peer_connected)
+	multiplayer.peer_disconnected.connect(_on_peer_disconnected)
+	multiplayer.connected_to_server.connect(_on_connection_ok)
+	multiplayer.connection_failed.connect(_on_connection_failed)
+	multiplayer.server_disconnected.connect(_on_server_disconnected)
+
+	# Auto-start from command line args
+	var args := OS.get_cmdline_user_args()
+	if "--server" in args:
+		start_dedicated_server(DEFAULT_PORT)
+	elif "--client" in args:
+		var idx := args.find("--client")
+		var address := "127.0.0.1"
+		if idx + 1 < args.size():
+			address = args[idx + 1]
+		join_server(address, DEFAULT_PORT)
+
+
+func start_dedicated_server(port: int = DEFAULT_PORT) -> bool:
+	peer = ENetMultiplayerPeer.new()
+	var err := peer.create_server(port, MAX_PLAYERS)
+	if err != OK:
+		push_error("NetworkManager: server creation failed — error %d" % err)
+		peer = null
+		return false
+	multiplayer.multiplayer_peer = peer
+	current_mode = Mode.DEDICATED
+	print("[NET] Dedicated server listening on port %d" % port)
+	server_started.emit()
+	return true
+
+
+func start_host(port: int = DEFAULT_PORT) -> bool:
+	peer = ENetMultiplayerPeer.new()
+	var err := peer.create_server(port, MAX_PLAYERS)
+	if err != OK:
+		push_error("NetworkManager: host creation failed — error %d" % err)
+		peer = null
+		return false
+	multiplayer.multiplayer_peer = peer
+	current_mode = Mode.HOST
+	print("[NET] Host server listening on port %d" % port)
+	server_started.emit()
+	return true
+
+
+func join_server(address: String, port: int = DEFAULT_PORT) -> bool:
+	peer = ENetMultiplayerPeer.new()
+	var err := peer.create_client(address, port)
+	if err != OK:
+		push_error("NetworkManager: client connection failed — error %d" % err)
+		peer = null
+		return false
+	multiplayer.multiplayer_peer = peer
+	current_mode = Mode.CLIENT
+	print("[NET] Connecting to %s:%d" % [address, port])
+	return true
+
+
+func disconnect_from_server() -> void:
+	if peer != null:
+		peer.close()
+		peer = null
+	multiplayer.multiplayer_peer = null
+	current_mode = Mode.NONE
+	server_closed.emit()
+
+
+func _on_peer_connected(id: int) -> void:
+	print("[NET] Peer connected: %d" % id)
+	peer_connected.emit(id)
+
+
+func _on_peer_disconnected(id: int) -> void:
+	print("[NET] Peer disconnected: %d" % id)
+	peer_disconnected.emit(id)
+
+
+func _on_connection_ok() -> void:
+	print("[NET] Connected to server (my id: %d)" % multiplayer.get_unique_id())
+	connection_succeeded.emit()
+
+
+func _on_connection_failed() -> void:
+	push_warning("[NET] Connection failed")
+	peer = null
+	multiplayer.multiplayer_peer = null
+	current_mode = Mode.NONE
+	connection_failed.emit()
+
+
+func _on_server_disconnected() -> void:
+	push_warning("[NET] Server disconnected")
+	peer = null
+	multiplayer.multiplayer_peer = null
+	current_mode = Mode.NONE
+	server_closed.emit()
+
+
+func is_server() -> bool:
+	return current_mode == Mode.HOST or current_mode == Mode.DEDICATED
+
+
+func is_client() -> bool:
+	return current_mode == Mode.CLIENT
+
+
+func is_solo() -> bool:
+	return current_mode == Mode.SOLO or current_mode == Mode.NONE
+
+
+func get_my_id() -> int:
+	return multiplayer.get_unique_id()