chore: core 多模块骨架

IosClientKit/Sources/CoreUI/PlaceholderView.swift

@@ -0,0 +1,16 @@
+import SwiftUI
+
+/// 尚未实现的 Tab 占位视图。
+public struct PlaceholderView: View {
+    private let title: String
+    private let systemImage: String
+
+    public init(_ title: String, systemImage: String) {
+        self.title = title
+        self.systemImage = systemImage
+    }
+
+    public var body: some View {
+        ContentUnavailableView(title, systemImage: systemImage)
+    }
+}