refactor(IOS-INFO-041): change default tab to sources + load on appear

- Set detailTab default to 1 (sources view)
- Load sources on appear via .task
- Refreshable reloads sources

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

AIStudyApp/AIStudyApp/Features/Library/LibrarySubpages.swift

@@ -141,7 +141,11 @@ struct LibraryDetailPage: View {
     @State private var isSelectMode = false
     @State private var selectedIds: Set<String> = []
     @State private var showBatchDeleteConfirm = false
-    @State private var detailTab = 0
+    @State private var detailTab = 1
+
+    private func appear() async {
+        await loadSources()
+    }
     @State private var sortOption = 0
     @State private var showFolderManager = false
     @State private var sources: [KnowledgeSource] = []
@@ -176,12 +180,6 @@ struct LibraryDetailPage: View {
                         .padding(.horizontal, 20).padding(.top, 8)
                 }
 
-                Picker("", selection: $detailTab) {
-                    Text("知识点").tag(0)
-                    Text("资料来源").tag(1)
-                }
-                .pickerStyle(.segmented)
-                .padding(.horizontal, 20).padding(.top, 12)
 
                 ScrollView {
                     VStack(spacing: 0) {
@@ -308,7 +306,7 @@ struct LibraryDetailPage: View {
                     .padding(.horizontal, 20).padding(.bottom, 80)
                 }
                 .scrollIndicators(.hidden)
-                .refreshable { await viewModel.refresh(knowledgeBaseId: knowledgeBaseId) }
+                .refreshable { await loadSources() }
             }
         }
         .navigationBarTitleDisplayMode(.inline).toolbarBackground(.hidden, for: .navigationBar).toolbar(.hidden, for: .tabBar)
@@ -411,7 +409,7 @@ struct LibraryDetailPage: View {
         } message: {
             Text("确定要删除选中的 \(selectedIds.count) 个知识点吗？此操作不可恢复。")
         }
-        .task { await viewModel.loadItems(knowledgeBaseId: knowledgeBaseId) }
+        .task { await appear() }
         .sheet(isPresented: $showFolderManager) {
             FolderManageView(knowledgeBaseId: knowledgeBaseId)
         }