feat(ios): W0 scaffold + day-1 spike + WireProtocol frozen contract + TestSupport doubles

T-iOS-1: ios/ XcodeGen project (iOS 17, Swift 6 strict concurrency, ATS per PLAN §5.2), 5 SPM package shells, CI skeleton
T-iOS-2: Origin spike vs real server — URLSessionWebSocketTask custom Origin CONFIRMED (no Starscream); 16MiB replay + EMSGSIZE(40) errno correction written back to plan
T-iOS-3: WireProtocol frozen contract, 59 tests, 100% line coverage, cross-impl vectors vs src/protocol.ts via tsx
T-iOS-4: FakeTransport/FakeClock/FakeHTTPTransport doubles
Verify: independent agent re-ran all acceptance — 6/6 PASS

ios/Packages/TestSupport/Package.swift

@@ -0,0 +1,21 @@
+// swift-tools-version: 6.0
+// T-iOS-4: test doubles leaned on by every W1-W3 task. Depends ONLY on
+// WireProtocol (the frozen contract) — never on SessionCore/HostRegistry/
+// APIClient, so it compiles in W0 and leaf packages stay decoupled (plan §6).
+import PackageDescription
+
+let package = Package(
+    name: "TestSupport",
+    platforms: [.iOS(.v17), .macOS(.v14)],
+    products: [
+        .library(name: "TestSupport", targets: ["TestSupport"]),
+    ],
+    dependencies: [
+        .package(path: "../WireProtocol"),
+    ],
+    targets: [
+        .target(name: "TestSupport", dependencies: ["WireProtocol"]),
+        .testTarget(name: "TestSupportTests", dependencies: ["TestSupport"]),
+    ],
+    swiftLanguageModes: [.v6]
+)