修复学习记录页面返回后数据不刷新，改为 viewWillAppear 重新加载统计

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

LearnEnglish/LearnEnglish/Views/HistoryViewController.swift

@@ -1,11 +1,10 @@
 import UIKit
 
 final class HistoryViewController: UITableViewController {
-    private let sections: [(title: String, items: [LearnedRecord])]
+    private var sections: [(title: String, items: [LearnedRecord])] = []
     private var speechObserver: NSObjectProtocol?
 
     init() {
-        sections = LearnedStore.shared.sectioned
         super.init(style: .plain)
     }
 
@@ -27,6 +26,18 @@ final class HistoryViewController: UITableViewController {
         tableView.backgroundColor = .systemBackground
         tableView.contentInset.top = 8
 
+        speechObserver = NotificationCenter.default.addObserver(
+            forName: SpeechService.speakingDidChangeNotification, object: nil, queue: .main
+        ) { [weak self] _ in
+            for cell in self?.tableView.visibleCells ?? [] {
+                (cell as? WordCardCell)?.updateSpeakerState()
+            }
+        }
+    }
+
+    override func viewWillAppear(_ animated: Bool) {
+        super.viewWillAppear(animated)
+        sections = LearnedStore.shared.sectioned
         if sections.isEmpty {
             let label = UILabel()
             label.text = "暂无学习记录"
@@ -41,15 +52,10 @@ final class HistoryViewController: UITableViewController {
                 label.centerYAnchor.constraint(equalTo: bg.centerYAnchor)
             ])
             tableView.backgroundView = bg
+        } else {
+            tableView.backgroundView = nil
         }
-
-        speechObserver = NotificationCenter.default.addObserver(
-            forName: SpeechService.speakingDidChangeNotification, object: nil, queue: .main
-        ) { [weak self] _ in
-            for cell in self?.tableView.visibleCells ?? [] {
-                (cell as? WordCardCell)?.updateSpeakerState()
-            }
-        }
+        tableView.reloadData()
     }
 
     override func numberOfSections(in tableView: UITableView) -> Int {