feat: feature 多模块骨架

IosClientKit/Sources/FeatureAuth/AuthScreen.swift

@@ -0,0 +1,10 @@
+import SwiftUI
+
+/// FeatureAuth 占位（后续实现登录 / 注册）。
+public struct AuthScreen: View {
+    public init() {}
+
+    public var body: some View {
+        ContentUnavailableView("登录", systemImage: "person.crop.circle")
+    }
+}