add a refresh action

ios/OralTrainer/Views/RootView.swift

@@ -14,6 +14,7 @@ struct RootView: View {
     @State private var courses: [Course] = []
     @State private var currentCourse: Course?
     @State private var courseStatusText = "正在同步"
+    @State private var isRefreshingCourses = false
     @State private var showCourseGuardToast = false
     @State private var managedResults: [UserResultSummary] = []
     @State private var managedDubShares: [UserDubShareSummary] = []
@@ -208,11 +209,29 @@ struct RootView: View {
                     .font(.system(size: 26, weight: .bold))
                     .foregroundColor(.white)
                     .padding(.horizontal, 16)
-                Text("选择一门课程开始训练")
-                    .font(.system(size: 13))
-                    .foregroundColor(Theme.textMuted)
-                    .padding(.horizontal, 16)
-                    .padding(.top, 4)
+                HStack(spacing: 10) {
+                    Text("选择一门课程开始训练")
+                        .font(.system(size: 13))
+                        .foregroundColor(Theme.textMuted)
+                    Spacer()
+                    Button {
+                        Task { await loadCourses() }
+                    } label: {
+                        Text(isRefreshingCourses ? "刷新中" : "刷新课程")
+                            .font(.system(size: 13, weight: .bold))
+                            .foregroundColor(.white)
+                            .padding(.horizontal, 12)
+                            .frame(height: 32)
+                            .background(Theme.buttonBlue)
+                            .clipShape(RoundedRectangle(cornerRadius: 8))
+                    }
+                    .buttonStyle(.plain)
+                    .disabled(isRefreshingCourses)
+                    .opacity(isRefreshingCourses ? 0.6 : 1)
+                    .padding(.trailing, 16)
+                }
+                .padding(.horizontal, 16)
+                .padding(.top, 4)
                 Text(courseStatusText)
                     .font(.system(size: 13))
                     .foregroundColor(Theme.textMuted)
@@ -509,10 +528,50 @@ struct RootView: View {
     // MARK: - Load Courses
 
     private func loadCourses() async {
+        guard !isRefreshingCourses else { return }
+        isRefreshingCourses = true
+        defer { isRefreshingCourses = false }
         courseStatusText = "正在同步"
         do {
-            courses = try await AuthAPI.courses(token: auth.token)
-            courseStatusText = "\(courses.count) 个课程"
+            var fetched = try await AuthAPI.courses(token: auth.token)
+            var boundarySucceeded = 0
+            var boundaryFailed = 0
+            courses = fetched
+            if !fetched.isEmpty {
+                courseStatusText = "\(fetched.count) 个课程，正在刷新句界"
+                let refreshed = await catalogVM.preloadBoundaries(
+                    for: fetched.map { $0.toVideoSummary() }
+                )
+                boundarySucceeded = refreshed.succeeded
+                boundaryFailed = refreshed.failed
+                let refreshedByHash = Dictionary(uniqueKeysWithValues: refreshed.videos.map { ($0.videoHash, $0) })
+                fetched = fetched.map { course in
+                    guard let video = refreshedByHash[course.videoHash] else { return course }
+                    return Course(
+                        videoHash: course.videoHash,
+                        title: course.title,
+                        durationMs: video.durationMs,
+                        language: course.language,
+                        sentenceCount: video.sentenceCount,
+                        streamUrl: course.streamUrl,
+                        enrolled: course.enrolled
+                    )
+                }
+                if currentCourse != nil,
+                   let video = refreshed.videos.first(where: { $0.videoHash == currentCourse?.videoHash }) {
+                    currentCourse = fetched.first(where: { $0.videoHash == video.videoHash })
+                }
+            }
+            courses = fetched
+            if fetched.isEmpty {
+                courseStatusText = "0 个课程"
+            } else if boundaryFailed == 0 {
+                courseStatusText = "\(fetched.count) 个课程 · 句界已刷新"
+            } else if boundarySucceeded == 0 {
+                courseStatusText = "\(fetched.count) 个课程 · 句界刷新失败"
+            } else {
+                courseStatusText = "\(fetched.count) 个课程 · 句界部分刷新（失败 \(boundaryFailed)）"
+            }
         } catch {
             courseStatusText = "课程加载失败：\(error.localizedDescription)"
         }