feat(avlivewire): shared wire package skeleton

shared/AVLiveWire/Package.swift

@@ -0,0 +1,14 @@
+// swift-tools-version:5.9
+import PackageDescription
+
+let package = Package(
+    name: "AVLiveWire",
+    platforms: [.macOS(.v13), .iOS(.v17)],
+    products: [
+        .library(name: "AVLiveWire", targets: ["AVLiveWire"]),
+    ],
+    targets: [
+        .target(name: "AVLiveWire"),
+        .testTarget(name: "AVLiveWireTests", dependencies: ["AVLiveWire"]),
+    ]
+)

shared/AVLiveWire/Sources/AVLiveWire/AVLiveWire.swift

@@ -0,0 +1,5 @@
+/// AVLiveWire — binary frame format shared by ARBodyTracker (iOS)
+/// and AVLiveBody (macOS) over the USB transport.
+public enum AVLiveWire {
+    public static let protocolVersion: UInt8 = 1
+}

shared/AVLiveWire/Tests/AVLiveWireTests/SmokeTests.swift

@@ -0,0 +1,8 @@
+import XCTest
+@testable import AVLiveWire
+
+final class SmokeTests: XCTestCase {
+    func testProtocolVersion() {
+        XCTAssertEqual(AVLiveWire.protocolVersion, 1)
+    }
+}