test(ios): real Swift compile + XCTest fixture; device-path probe; loopback bind fix

Closes the gap from prior commits where E2E tests stubbed the Swift StateServer
in TypeScript. Now there's a real SwiftPM fixture at test/fixtures/ios-qa/FixtureApp/
that compiles the production templates and runs an XCTest suite against the
actual StateServer implementation. Three new test layers:

- swift build invariants (periodic-tier): debug-config build succeeds, XCTest
  suite passes (validates real Swift impl over Foundation + Network), release-config
  build has zero DebugBridge symbols (structural #if DEBUG gate works end-to-end).

- Real-device probe (periodic-tier, GSTACK_HAS_IOS_DEVICE=1): devicectl can list
  + pair the connected iPhone. Surfaces actionable instructions when the trust
  dialog hasn't been confirmed yet.

- Fixture sources copied from ios-qa/templates/ — Package.swift splits the
  bridge into DebugBridgeCore (Foundation+Network, cross-platform) and
  DebugBridgeUI (UIKit/SwiftUI, iOS-only) so swift build can validate the
  bulk of the production code on macOS without an iPhone or simulator.

Also fixes a real bug the XCTest unit suite caught: NWListener with
requiredLocalEndpoint on params silently fails to bind for listening (it's
an outbound-connection concept). Replaced with .requiredInterfaceType=.loopback
+ .acceptLocalOnly=true + a per-connection peer-address check. The fork's
inherited code had this bug; we shipped it untouched in v1.41.0.0 and the
new XCTest suite caught it immediately.

test/fixtures/ios-qa/FixtureApp/Sources/DebugBridgeUI/DebugOverlay.swift

@@ -0,0 +1,137 @@
+// AUTO-GENERATED from gstack/ios-qa/templates/DebugOverlay.swift.template
+//
+// DebugOverlay — on-device visual presence. Animated brand-colored border +
+// agent attribution chip + (optional) recording watermark. Renders above
+// sheets, alerts, and modals via a dedicated UIWindow with high windowLevel.
+//
+// Everything in this file is gated #if DEBUG and gone in Release.
+
+#if DEBUG && canImport(UIKit)
+
+import SwiftUI
+import UIKit
+
+@MainActor
+public final class DebugOverlayWindow {
+    public static let shared = DebugOverlayWindow()
+
+    private var window: UIWindow?
+
+    public func install(recording: Bool = false) {
+        guard window == nil else { return }
+        guard let scene = UIApplication.shared.connectedScenes.compactMap({ $0 as? UIWindowScene }).first else { return }
+
+        let w = PassThroughWindow(windowScene: scene)
+        w.windowLevel = .alert + 1
+        w.backgroundColor = .clear
+        w.isUserInteractionEnabled = false
+
+        let host = UIHostingController(rootView: OverlayRoot(recording: recording))
+        host.view.backgroundColor = .clear
+        w.rootViewController = host
+        w.isHidden = false
+
+        window = w
+    }
+
+    public func setAttribution(_ identity: String) {
+        OverlayAttributionState.shared.identity = identity
+    }
+}
+
+/// A window that lets touches pass through to underlying windows.
+private final class PassThroughWindow: UIWindow {
+    override func hitTest(_ point: CGPoint, with event: UIEvent?) -> UIView? {
+        let view = super.hitTest(point, with: event)
+        return view == rootViewController?.view ? nil : view
+    }
+}
+
+@MainActor
+final class OverlayAttributionState: ObservableObject {
+    static let shared = OverlayAttributionState()
+    @Published var identity: String = "Claude Code (local)"
+}
+
+private struct OverlayRoot: View {
+    @StateObject private var attribution = OverlayAttributionState.shared
+    @State private var phase: CGFloat = 0
+    let recording: Bool
+
+    var body: some View {
+        ZStack {
+            // Animated brand border
+            BorderShape()
+                .stroke(
+                    AngularGradient(
+                        gradient: Gradient(colors: [
+                            BrandColor.accent.opacity(0.0),
+                            BrandColor.accent.opacity(0.8),
+                            BrandColor.accent.opacity(0.0),
+                        ]),
+                        center: .center,
+                        angle: .degrees(phase * 360)
+                    ),
+                    lineWidth: 4
+                )
+                .ignoresSafeArea()
+                .onAppear {
+                    withAnimation(.linear(duration: 2.0).repeatForever(autoreverses: false)) {
+                        phase = 1.0
+                    }
+                }
+
+            // Attribution chip (top safe area)
+            VStack {
+                HStack {
+                    Spacer()
+                    Text("Driven by \(attribution.identity)")
+                        .font(.caption2.weight(.semibold))
+                        .foregroundColor(.white)
+                        .padding(.horizontal, 10)
+                        .padding(.vertical, 4)
+                        .background(
+                            Capsule().fill(BrandColor.accent.opacity(0.85))
+                        )
+                        .padding(.trailing, 12)
+                        .padding(.top, 8)
+                    Spacer().frame(width: 0)
+                }
+                Spacer()
+            }
+
+            // Recording watermark (diagonal, bottom-right)
+            if recording {
+                VStack {
+                    Spacer()
+                    HStack {
+                        Spacer()
+                        Text("AGENT DEMO")
+                            .font(.system(size: 10, weight: .heavy, design: .monospaced))
+                            .foregroundColor(.red.opacity(0.7))
+                            .rotationEffect(.degrees(-30))
+                            .padding(.trailing, 16)
+                            .padding(.bottom, 30)
+                    }
+                }
+            }
+        }
+        .allowsHitTesting(false)
+    }
+}
+
+private struct BorderShape: Shape {
+    func path(in rect: CGRect) -> Path {
+        var p = Path()
+        p.addRoundedRect(in: rect.insetBy(dx: 2, dy: 2), cornerSize: CGSize(width: 16, height: 16))
+        return p
+    }
+}
+
+private enum BrandColor {
+    // gstack brand color — resolved from DESIGN.md when codegen runs.
+    // Default falls back to a deep blue.
+    static let accent = Color(red: 0.0, green: 0.46, blue: 1.0)
+}
+
+#endif // DEBUG && canImport(UIKit)