Establish watch relay contracts and platform package wiring

Adapters/WatchBridge/Sources/Common/RelayContainer.swift

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+import Foundation
+import RemoteCore
+
+/// Typed outgoing container seam. Workstream B owns WCSession dictionary parsing,
+/// strict incoming key/type validation, routing and exactly-once replies.
+public struct RelayContainer: Sendable {
+    public let schemaVersion = RelayWire.schemaVersion
+    public let kind: RelayMessageKind
+    public let payload: Data
+
+    public init<Value: Encodable>(kind: RelayMessageKind, value: Value) throws {
+        self.kind = kind
+        self.payload = try RelayJSON.encode(value)
+    }
+}

Adapters/WatchBridge/Sources/Watch/WatchCommandPayload.swift

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+import RemoteCore
+import WatchBridgeCommon
+
+/// Pure outgoing container construction: does not activate WCSession, grant a
+/// session, queue a command, or transmit it. Live delivery belongs to B.
+public enum WatchCommandPayload {
+    public static func container(for envelope: CommandEnvelope) throws -> RelayContainer {
+        try RelayContainer(kind: .command, value: envelope)
+    }
+}

Adapters/WatchBridge/Sources/iPhone/PhoneRelayDependency.swift

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+import RemoteCore
+
+/// An injection seam, not a live relay. App composition supplies the same actor
+/// used for phone commands; this holder creates no admission or session state.
+public struct PhoneRelayDependency: Sendable {
+    public let coordinator: any PhoneCommandCoordinating
+
+    public init(coordinator: any PhoneCommandCoordinating) {
+        self.coordinator = coordinator
+    }
+}