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/SessionCore/Tests/SessionCoreTests/PackageScaffoldTests.swift

@@ -0,0 +1,13 @@
+import Testing
+import SessionCore
+
+@Test("脚手架:SessionCore 包可编译且依赖边 SessionCore→WireProtocol 成立")
+func sessionCorePackageIsImportableAndDependsOnWireProtocol() {
+    // Arrange / Act
+    let name = SessionCorePackage.packageName
+    let contract = SessionCorePackage.contractPackageName
+
+    // Assert
+    #expect(name == "SessionCore")
+    #expect(contract == "WireProtocol")
+}