fix: 修复导出诊断包点击后黑屏问题

将 .sheet(isPresented:) + if let 改为 .sheet(item:) 模式，
消除 feedbackPackageURL 与 showingShareSheet 的状态时序竞争。

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

to-live-photo/to-live-photo/Views/SettingsView.swift

@@ -13,8 +13,7 @@ struct SettingsView: View {
     @State private var cacheSize: String = String(localized: "common.calculating")
     @State private var showingClearCacheAlert = false
     @State private var showingClearRecentWorksAlert = false
-    @State private var feedbackPackageURL: URL?
-    @State private var showingShareSheet = false
+    @State private var feedbackPackageURL: IdentifiableURL?
     @State private var showingLanguageChangeAlert = false
     @State private var showingFeedbackConfirmAlert = false
     @State private var pendingLanguage: LanguageManager.Language?
@@ -182,10 +181,8 @@ struct SettingsView: View {
         } message: {
             Text(String(localized: "settings.feedbackConfirmMessage"))
         }
-        .sheet(isPresented: $showingShareSheet) {
-            if let url = feedbackPackageURL {
-                ShareSheet(activityItems: [url])
-            }
+        .sheet(item: $feedbackPackageURL) { item in
+            ShareSheet(activityItems: [item.url])
         }
     }
 
@@ -299,8 +296,7 @@ struct SettingsView: View {
             let url = await createFeedbackPackage()
             await MainActor.run {
                 if let url {
-                    feedbackPackageURL = url
-                    showingShareSheet = true
+                    feedbackPackageURL = IdentifiableURL(url: url)
                 }
             }
         }
@@ -425,6 +421,12 @@ extension PHAuthorizationStatus: @retroactive CustomStringConvertible {
     }
 }
 
+// MARK: - Identifiable URL Wrapper
+struct IdentifiableURL: Identifiable {
+    let id = UUID()
+    let url: URL
+}
+
 // MARK: - Share Sheet
 struct ShareSheet: UIViewControllerRepresentable {
     let activityItems: [Any]