feat: feature 多模块骨架

IosClientKit/Sources/FeatureAuth/AuthScreen.swift

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+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")
+    }
+}

IosClientKit/Sources/FeatureHome/HomeScreen.swift

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+import SwiftUI
+import CoreModel
+import CoreUI
+import DesignSystem
+
+public struct HomeScreen: View {
+    private let viewModel: HomeViewModel
+
+    public init(viewModel: HomeViewModel) {
+        self.viewModel = viewModel
+    }
+
+    public var body: some View {
+        content
+            .navigationTitle("首页")
+            .task { viewModel.load() }
+    }
+
+    @ViewBuilder
+    private var content: some View {
+        switch viewModel.uiState {
+        case .loading:
+            LoadingView()
+        case .empty:
+            EmptyStateView(title: "今天还没有待打卡的习惯", systemImage: "checkmark.circle")
+        case .success(let data):
+            successContent(data)
+        case .error(let message):
+            ErrorView(message: message) { viewModel.load() }
+        }
+    }
+
+    private func successContent(_ data: HomeData) -> some View {
+        List {
+            Section {
+                VStack(alignment: .leading, spacing: DS.Spacing.sm) {
+                    Text(data.greeting)
+                        .font(.largeTitle.bold())
+                    Text(data.summary)
+                        .font(.subheadline)
+                        .foregroundStyle(.secondary)
+                }
+                .padding(.vertical, DS.Spacing.sm)
+            }
+
+            Section("今日打卡") {
+                ForEach(data.habits) { habit in
+                    HabitRow(habit: habit)
+                }
+            }
+        }
+    }
+}
+
+private struct HabitRow: View {
+    let habit: Habit
+
+    var body: some View {
+        HStack {
+            Image(systemName: habit.isCheckedInToday ? "checkmark.circle.fill" : "circle")
+                .foregroundStyle(habit.isCheckedInToday ? DS.Color.success : DS.Color.warning)
+                .font(.title3)
+            VStack(alignment: .leading, spacing: 2) {
+                Text(habit.title)
+                    .font(.headline)
+                Text(habit.detail)
+                    .font(.caption)
+                    .foregroundStyle(.secondary)
+            }
+            Spacer()
+            Text("🔥 \(habit.streakDays) 天")
+                .font(.caption)
+                .foregroundStyle(.secondary)
+        }
+        .padding(.vertical, DS.Spacing.xs)
+    }
+}

IosClientKit/Sources/FeatureHome/HomeUiState.swift

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+import CoreModel
+
+/// Kotlin: sealed interface HomeUiState → Swift: enum 关联值
+public enum HomeUiState {
+    case loading
+    case success(HomeData)
+    case empty
+    case error(String)
+}

IosClientKit/Sources/FeatureHome/HomeViewModel.swift

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+import CoreDomain
+import CoreModel
+import Observation
+
+@MainActor
+@Observable
+public final class HomeViewModel {
+    public private(set) var uiState: HomeUiState = .loading
+
+    private let homeUseCase: HomeUseCase
+    private var loadTask: Task<Void, Never>?
+
+    public init(homeUseCase: HomeUseCase) {
+        self.homeUseCase = homeUseCase
+    }
+
+    public func load() {
+        // flatMapLatest 的等价：新 load 前先取消旧的观察。
+        loadTask?.cancel()
+        loadTask = Task { [weak self] in
+            guard let self else { return }
+            self.uiState = .loading
+            do {
+                for try await data in self.homeUseCase.observeHome() {
+                    self.uiState = data.habits.isEmpty ? .empty : .success(data)
+                }
+            } catch is CancellationError {
+                // 被更新的 load() 取代，保持当前状态即可。
+            } catch {
+                self.uiState = .error(error.localizedDescription)
+            }
+        }
+    }
+}