fix(IOS-INFO-041): load KB info on appear + fix initial loading state

- Set isLoadingSources = true initially to show spinner
- Load KnowledgeBase detail in appear() for header
- Prevents blank screen before data loads

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

AIStudyApp/AIStudyApp/Features/Library/LibrarySubpages.swift

@@ -144,13 +144,15 @@ struct LibraryDetailPage: View {
     @State private var detailTab = 1
 
     private func appear() async {
+        // Load KB info and sources
+        viewModel.knowledgeBase = try? await KnowledgeBaseService.shared.detail(id: knowledgeBaseId)
         await loadSources()
     }
     @State private var sortOption = 0
     @State private var showFolderManager = false
     @State private var sources: [KnowledgeSource] = []
     @State private var sourceReadingStatus: [String: String] = [:]
-    @State private var isLoadingSources = false
+    @State private var isLoadingSources = true
 
     private var allSelected: Bool {
         !viewModel.items.isEmpty && selectedIds.count == viewModel.items.count