fix(client): batch-encode inputs as Vec<PlayerInput> per server wire format

Server expects a MessagePack array of PlayerInput objects in one framed
message per tick, not individual inputs per frame. Added
Protocol.encode_player_inputs() for batch encoding. Changed SimBridge to
buffer raw input dicts and batch-encode in _process(). Also fixed server
port default (9876) and positional arg format to match server CLI.

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

client/scripts/protocol/protocol.gd

@@ -107,6 +107,32 @@ static func encode_player_input(tick: int, action_name: String, action_data: Var
 	return result.value
 
 
+## Encode an array of PlayerInputs to MessagePack bytes (Vec<PlayerInput> wire format).
+## Server expects one framed message per tick containing all inputs as a msgpack array.
+## Each entry: { "tick": int, "action_name": String, "action_data": Variant (optional) }
+static func encode_player_inputs(inputs: Array) -> PackedByteArray:
+	var wire_inputs: Array = []
+	for input in inputs:
+		var action_name: String = input["action_name"]
+		var action_data: Variant = input.get("action_data")
+		var action_value: Variant
+		if action_data != null:
+			action_value = { action_name: action_data }
+		else:
+			action_value = action_name
+		wire_inputs.append({
+			"tick": input["tick"],
+			"action": action_value,
+		})
+
+	var result = Messagepack.encode(wire_inputs)
+	if result.status != null:
+		push_error("Protocol: msgpack encode failed: %s" % result.status)
+		return PackedByteArray()
+
+	return result.value
+
+
 ## Decode a PlayerInput from MessagePack bytes (used in tests / echo scenarios).
 ## Returns { "tick": int, "action": { "variant": String, "data": Variant } } or null.
 static func decode_player_input(bytes: PackedByteArray) -> Variant: