feat(chat): share SwiftUI chat across macOS+iOS

apps/shared/ClawdisKit/Sources/ClawdisChatUI/ChatTransport.swift

@@ -0,0 +1,27 @@
+import Foundation
+
+public enum ClawdisChatTransportEvent: Sendable {
+    case health(ok: Bool)
+    case tick
+    case chat(ClawdisChatEventPayload)
+    case seqGap
+}
+
+public protocol ClawdisChatTransport: Sendable {
+    func requestHistory(sessionKey: String) async throws -> ClawdisChatHistoryPayload
+    func sendMessage(
+        sessionKey: String,
+        message: String,
+        thinking: String,
+        idempotencyKey: String,
+        attachments: [ClawdisChatAttachmentPayload]) async throws -> ClawdisChatSendResponse
+
+    func requestHealth(timeoutMs: Int) async throws -> Bool
+    func events() -> AsyncStream<ClawdisChatTransportEvent>
+
+    func setActiveSessionKey(_ sessionKey: String) async throws
+}
+
+extension ClawdisChatTransport {
+    public func setActiveSessionKey(_: String) async throws {}
+}