feat(ios): 中继通道 P4/P5——端点抽象、信封、传输、配对与分层错误

- InstanceEndpoint 取代 Instance.origin（旧数据 init(from:) 读成 .direct，
  写盘只输出 endpoint；dedupKey 直通用 origin、中继用 relay:<nodeID>）
- RelayWire：Swift 侧重算 contracts/test-vectors.json（CanonicalJSON 手写解析器，
  因为 Foundation 的解码器会抹掉'拼写'，而 intent 摘要定义的正是拼写）
- NodeTransport 抽象 + DirectTransport / RelayTransport / NodeTransportRouter；
  DirectTransport 是薄适配，直通路径行为不变
- RelayTransport：信封构造、签名、加密、验签、解密；响应验签失败即丢弃，
  四类以上失败各有独立 UpstreamError 分支与用户文案
- DeviceIdentity（沙盒文件 0600，配对时由节点分配 deviceID）、RelayPairing、配对 sheet
- 卡片通道徽标 + freshness 副标题；危险写 intent 在发送瞬间生成
- scripts/export-app-routes.swift 生成 vendored 路由表，AppRoutesContractTests 反向守卫
- 测试 78→92：向量互算、迁移（字面量旧 JSON）、配对四类失败、路由器、
  传输往返与各类拒绝路径

apps/ios/Sources/MultiSimAdmin/Features/Fleet/FleetViewModel.swift

@@ -29,6 +29,19 @@ final class FleetViewModel: ObservableObject {
         var uptimeSeconds: Double?
         var chainValues: DeviceLinkState?
         var testing: Bool
+        /// Why the last probe ended where it did, for the detail text.
+        var probeError: UpstreamError?
+        /// When the last probe finished. The list shows how old a reading is, which in relay mode is
+        /// the difference between "online" meaning now and meaning forty seconds ago.
+        var checkedAt: Date?
+
+        /// Which path this node is reached by. The badge exists because without it "this one is
+        /// slow" has no answer that a user can act on.
+        var channel: InstanceChannel { instance.endpoint.channel }
+
+        var freshness: SnapshotFreshness {
+            testing ? .unknown : SnapshotFreshness.classify(age: checkedAt.map { Date().timeIntervalSince($0) })
+        }
 
         var storageUsageRatio: Double? {
             guard let total = totalStorageBytes, let available = availableStorageBytes, total > 0 else {
@@ -143,7 +156,7 @@ final class FleetViewModel: ObservableObject {
             expectedRevision: original.instance.configRevision,
             InstancePatch(
                 name: input.name,
-                origin: input.origin,
+                endpoint: input.endpoint,
                 tags: input.tags,
                 password: input.password
             )
@@ -215,6 +228,8 @@ final class FleetViewModel: ObservableObject {
     ) {
         guard let index = rows.firstIndex(where: { $0.id == id }) else { return }
         rows[index].status = result?.status ?? .unknown
+        rows[index].probeError = result?.error
+        rows[index].checkedAt = result?.checkedAt
         if let summary {
             rows[index].deviceName = summary.deviceName
             rows[index].phoneNumber = summary.phoneNumber
@@ -260,7 +275,7 @@ final class FleetViewModel: ObservableObject {
             guard !searchText.isEmpty else { return true }
             let haystacks: [String] = [
                 row.instance.name,
-                row.instance.origin.absoluteString,
+                row.instance.endpoint.displayAddress,
                 row.instance.tags.joined(separator: " "),
                 row.operatorName ?? "",
                 row.phoneNumber ?? "",