fix(ios): 修复顶部导航栏间距过大问题

- 所有 Tab 主页面 padding-top 从 statusBarH(44)+16=60pt 改为 8pt
- NavigationStack 已自动处理状态栏安全区，无需手动硬编码
- 影响页面：StudyHomeView / LibraryHomeView / AnalysisHomeView / ProfileView

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

AIStudyApp/AIStudyApp/Features/Analysis/AnalysisHomeView.swift

@@ -12,7 +12,7 @@ struct AnalysisHomeView: View {
                     HStack(spacing: 4) { Text("近 7 天").font(.system(size: 12)).foregroundColor(Color.zxF05); Image(systemName: "chevron.down").font(.system(size: 10)).foregroundColor(Color.zxF04) }
                         .padding(.horizontal, 12).padding(.vertical, 6).background(Color.zxFill005).clipShape(Capsule()).overlay(Capsule().stroke(Color.zxBorder008, lineWidth: 1))
                 }
-                .padding(.horizontal, 20).padding(.top, ZXSpacing.statusBarH + 16).padding(.bottom, 12)
+                .padding(.horizontal, 20).padding(.top, 8).padding(.bottom, 12)
                 ScrollView {
                     VStack(spacing: 16) {
                         if viewModel.isLoading && viewModel.summary == nil {

AIStudyApp/AIStudyApp/Features/Library/LibraryHomeView.swift

@@ -25,7 +25,7 @@ struct LibraryHomeView: View {
                     }
                     .accessibilityLabel("导入新知识库")
                 }
-                    .padding(.horizontal, 20).padding(.top, ZXSpacing.statusBarH + 16).padding(.bottom, 12)
+                    .padding(.horizontal, 20).padding(.top, 8).padding(.bottom, 12)
                 HStack(spacing: 8) { Image(systemName: "magnifyingglass").font(.system(size: 16)).foregroundColor(Color.zxF03); TextField("搜索知识库或知识点…", text: $s).font(.system(size: 14)).tint(Color.zxPurple).accessibilityLabel("搜索知识库") }
                     .padding(.horizontal, 14).frame(height: 44).background(Color.zxFill004).overlay(RoundedRectangle(cornerRadius: 14).stroke(Color.zxBorder008, lineWidth: 1)).clipShape(RoundedRectangle(cornerRadius: 14)).padding(.horizontal, 20).padding(.bottom, 16)
                     .accessibilityHint("输入关键词搜索知识库或知识点")

AIStudyApp/AIStudyApp/Features/Profile/ProfileView.swift

@@ -25,7 +25,7 @@ struct ProfileView: View {
                                 .overlay(RoundedRectangle(cornerRadius: 10).stroke(Color.zxBorder008, lineWidth: 1))
                         }
                         .accessibilityLabel("设置")
-                    }.padding(.horizontal, 20).padding(.top, ZXSpacing.statusBarH + 16).padding(.bottom, 4)
+                    }.padding(.horizontal, 20).padding(.top, 8).padding(.bottom, 4)
                     profileCard
                     VStack(spacing: 0) {
                         NavigationLink(value: Route.goalSetting) {

AIStudyApp/AIStudyApp/Features/Study/StudyHomeView.swift

@@ -32,7 +32,7 @@ struct StudyHomeView: View {
                         .overlay(Capsule().stroke(Color(hex: "#F97316", opacity: 0.2), lineWidth: 1))
                     }
                     .padding(.horizontal, 20)
-                    .padding(.top, ZXSpacing.statusBarH + 16)
+                    .padding(.top, 8)
                     .padding(.bottom, 4)
 
                     // MARK: - Progress