feat(avlivebody-mac): scaffold xcode app

Add an empty buildable native macOS app generated via xcodegen,
sibling of iphone-arbody. Depends on the shared AVLiveWire package.
Later tasks add the USB pipeline and RealityKit scene.

avlivebody-mac/.gitignore

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+*.xcodeproj/
+Config/Local.xcconfig
+.build/
+.swiftpm/

avlivebody-mac/Config/Local.xcconfig.example

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+// Copy to Config/Local.xcconfig and set your Apple Developer Team ID.
+// Config/Local.xcconfig is gitignored.
+DEVELOPMENT_TEAM = YOUR_TEAM_ID

avlivebody-mac/Config/Shared.xcconfig

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+#include? "Local.xcconfig"
+
+MACOSX_DEPLOYMENT_TARGET = 15.0
+SWIFT_VERSION = 5.10
+CODE_SIGN_STYLE = Automatic

avlivebody-mac/Sources/AVLiveBody/AVLiveBodyApp.swift

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+import Cocoa
+import SwiftUI
+
+/// Forces a regular, keyboard-focusable foreground app.
+final class AppDelegate: NSObject, NSApplicationDelegate {
+    func applicationDidFinishLaunching(_ notification: Notification) {
+        NSApp.setActivationPolicy(.regular)
+        NSApp.activate()
+    }
+}
+
+@main
+struct AVLiveBodyApp: App {
+    @NSApplicationDelegateAdaptor(AppDelegate.self)
+    private var appDelegate
+
+    var body: some Scene {
+        WindowGroup {
+            Text("AVLiveBody")
+                .frame(minWidth: 900, minHeight: 600)
+        }
+    }
+}

avlivebody-mac/Sources/AVLiveBody/Info.plist

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+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
+<plist version="1.0">
+<dict>
+    <key>CFBundleName</key><string>AVLiveBody</string>
+    <key>CFBundleIdentifier</key><string>$(PRODUCT_BUNDLE_IDENTIFIER)</string>
+    <key>CFBundleExecutable</key><string>$(EXECUTABLE_NAME)</string>
+    <key>CFBundlePackageType</key><string>APPL</string>
+    <key>CFBundleShortVersionString</key><string>1.0</string>
+    <key>CFBundleVersion</key><string>1</string>
+    <key>LSMinimumSystemVersion</key><string>15.0</string>
+    <key>NSCameraUsageDescription</key>
+    <string>Receives the tethered iPhone camera over USB.</string>
+    <key>NSLocalNetworkUsageDescription</key>
+    <string>Connects to the tethered iPhone over USB (usbmuxd).</string>
+</dict>
+</plist>

avlivebody-mac/project.yml

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+name: AVLiveBody
+options:
+  bundleIdPrefix: cc.saillant
+  deploymentTarget:
+    macOS: "15.0"
+  createIntermediateGroups: true
+
+configFiles:
+  Debug: Config/Shared.xcconfig
+  Release: Config/Shared.xcconfig
+
+packages:
+  AVLiveWire:
+    path: ../shared/AVLiveWire
+
+targets:
+  AVLiveBody:
+    type: application
+    platform: macOS
+    deploymentTarget: "15.0"
+    sources:
+      - path: Sources/AVLiveBody
+        excludes:
+          - Info.plist
+    dependencies:
+      - package: AVLiveWire
+        product: AVLiveWire
+    configFiles:
+      Debug: Config/Shared.xcconfig
+      Release: Config/Shared.xcconfig
+    settings:
+      base:
+        PRODUCT_NAME: AVLiveBody
+        PRODUCT_BUNDLE_IDENTIFIER: cc.saillant.AVLiveBody
+        INFOPLIST_FILE: Sources/AVLiveBody/Info.plist
+        GENERATE_INFOPLIST_FILE: NO
+        CODE_SIGN_STYLE: Automatic
+        SWIFT_VERSION: "5.10"
+        ENABLE_HARDENED_RUNTIME: YES
+  AVLiveBodyTests:
+    type: bundle.unit-test
+    platform: macOS
+    sources:
+      - path: Tests/AVLiveBodyTests
+    dependencies:
+      - target: AVLiveBody
+      - package: AVLiveWire
+        product: AVLiveWire