feat(ios): 封面图底部半屏抽屉弹窗 + 左侧正方形卡片

- 封面图有独立中文标签"封面图"
- 120×120 正方形虚线框，左侧对齐
- 点击弹出底部半屏 sheet（height: 220）
- sheet 内：从相册选择（带图标+描述+箭头）
- 顶部有指示条（灰色胶囊）

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

AIStudyApp/AIStudyApp/Features/Library/LibrarySubpages.swift

@@ -12,29 +12,28 @@ struct CreateLibraryPage: View {
     var body: some View {
         ZStack { Color.zxBg0.ignoresSafeArea(); VStack(spacing: 0) {
             ScrollView { VStack(spacing: 20) {
-                // 封面卡片
+                // 封面图
-                Button { showCoverSheet = true } label: {
+                VStack(alignment: .leading, spacing: 8) {
-                    ZStack {
+                    Text("封面图").font(.system(size: 12, weight: .semibold)).foregroundColor(Color.zxF035)
-                        RoundedRectangle(cornerRadius: 14).fill(Color.zxFill004)
+                    Button { showCoverSheet = true } label: {
-                            .overlay(RoundedRectangle(cornerRadius: 14).stroke(Color.zxBorder008, lineWidth: 1))
+                        ZStack {
-                        if let img = coverImage {
+                            RoundedRectangle(cornerRadius: 14).fill(Color.zxFill004)
-                            Image(uiImage: img).resizable().scaledToFill().frame(height: 140).clipShape(RoundedRectangle(cornerRadius: 14))
+                                .overlay(RoundedRectangle(cornerRadius: 14).stroke(style: StrokeStyle(lineWidth: 1.5, dash: [6, 4])).foregroundColor(Color.zxBorder01))
-                        } else {
+                                .frame(width: 120, height: 120)
-                            VStack(spacing: 8) {
+                            if let img = coverImage {
-                                Image(systemName: "photo.on.rectangle.angled").font(.system(size: 28)).foregroundColor(Color.zxF04)
+                                Image(uiImage: img).resizable().scaledToFill().frame(width: 120, height: 120).clipShape(RoundedRectangle(cornerRadius: 14))
-                                Text("添加封面图").font(.system(size: 13, weight: .medium)).foregroundColor(Color.zxF04)
+                            } else {
-                                Text("从相册选择").font(.system(size: 11)).foregroundColor(Color.zxF03)
+                                VStack(spacing: 6) {
+                                    Image(systemName: "camera.fill").font(.system(size: 22)).foregroundColor(Color.zxF04)
+                                    Text("上传").font(.system(size: 11)).foregroundColor(Color.zxF04)
+                                }
                             }
+                            if isUploadingCover { RoundedRectangle(cornerRadius: 14).fill(Color.black.opacity(0.4)).frame(width: 120, height: 120); ProgressView().tint(.white) }
                         }
-                        if isUploadingCover { RoundedRectangle(cornerRadius: 14).fill(Color.black.opacity(0.4)); ProgressView().tint(.white) }
                     }
-                    .frame(height: 140)
+                    .disabled(isUploadingCover)
-                }
-                .disabled(isUploadingCover)
-                .confirmationDialog("封面图", isPresented: $showCoverSheet) {
-                    Button("从相册选择") { showCoverPicker = true }
-                    Button("取消", role: .cancel) {}
                 }
+                .frame(maxWidth: .infinity, alignment: .leading)
 
                 VStack(alignment: .leading, spacing: 8) {
                     HStack(spacing: 2) { Text("知识库名称").font(.system(size: 12, weight: .semibold)); Text("*").foregroundColor(.red) }.foregroundColor(Color.zxF035)
@@ -78,6 +77,35 @@ struct CreateLibraryPage: View {
         .onChange(of: coverPhotoItem) { _, item in
             guard let item else { return }
             Task { await uploadCover(item) }
+        }
+        .sheet(isPresented: $showCoverSheet) {
+            VStack(spacing: 0) {
+                RoundedRectangle(cornerRadius: 3).fill(Color.zxF03).frame(width: 36, height: 5).padding(.top, 12).padding(.bottom, 16)
+                Text("封面图").font(.system(size: 16, weight: .semibold)).foregroundColor(Color.zxF0).padding(.bottom, 20)
+                Button {
+                    showCoverSheet = false
+                    DispatchQueue.main.asyncAfter(deadline: .now() + 0.3) { showCoverPicker = true }
+                } label: {
+                    HStack(spacing: 12) {
+                        Image(systemName: "photo.on.rectangle").font(.system(size: 20)).foregroundColor(Color.zxPrimary).frame(width: 40, height: 40).background(Color.zxPrimarySoft).clipShape(RoundedRectangle(cornerRadius: 10))
+                        VStack(alignment: .leading, spacing: 2) {
+                            Text("从相册选择").font(.system(size: 15, weight: .medium)).foregroundColor(Color.zxF0)
+                            Text("选择一张图片作为封面").font(.system(size: 12)).foregroundColor(Color.zxF04)
+                        }
+                        Spacer()
+                        Image(systemName: "chevron.right").font(.system(size: 14)).foregroundColor(Color.zxF03)
+                    }
+                    .padding(.horizontal, 16).padding(.vertical, 14)
+                    .background(Color.zxFill004).clipShape(RoundedRectangle(cornerRadius: 14))
+                }
+                .foregroundColor(.primary)
+                .padding(.horizontal, 20)
+                Spacer()
+            }
+            .frame(maxWidth: .infinity, maxHeight: .infinity)
+            .background(Color.zxBg0)
+            .presentationDetents([.height(220)])
+            .presentationDragIndicator(.hidden)
         }}
 
     private func uploadCover(_ item: PhotosPickerItem) async {