新增阅读器功能，待优化

lib/service/book_import_service.dart

@@ -0,0 +1,75 @@
+import 'dart:io';
+import 'package:file_picker/file_picker.dart';
+import 'package:flutter/material.dart';
+import 'package:path/path.dart' as p;
+import 'package:uuid/uuid.dart';
+import '../models/reader_book.dart';
+import '../providers/app_provider.dart';
+import '../utils/book_file_helper.dart';
+
+/// 书籍导入服务
+class BookImportService {
+  static const allowedExtensions = ['epub', 'txt'];
+
+  static Future<ReaderBook?> pickAndImportBook(
+    BuildContext context,
+    AppProvider provider,
+  ) async {
+    final result = await FilePicker.platform.pickFiles(
+      type: FileType.custom,
+      allowedExtensions: allowedExtensions,
+      allowMultiple: false,
+    );
+
+    if (result == null || result.files.isEmpty) return null;
+
+    final platformFile = result.files.first;
+    final sourcePath = platformFile.path;
+    if (sourcePath == null) return null;
+
+    final file = File(sourcePath);
+    if (!await file.exists()) return null;
+
+    final extension = p.extension(file.path).replaceAll('.', '').toLowerCase();
+    if (!allowedExtensions.contains(extension)) {
+      if (context.mounted) {
+        ScaffoldMessenger.of(context).showSnackBar(
+          SnackBar(content: Text('不支持的格式：$extension')),
+        );
+      }
+      return null;
+    }
+
+    final title = p.basenameWithoutExtension(platformFile.name);
+    final helper = BookFileHelper.instance;
+    final id = const Uuid().v4();
+
+    // 清理文件名，去除特殊字符
+    final safeName = platformFile.name.replaceAll(RegExp(r'[<>:"/\\|?*]'), '_');
+    final destPath = await helper.bookFile(id, safeName);
+
+    // 复制文件
+    await file.copy(destPath);
+
+    final now = DateTime.now();
+    final readerBook = ReaderBook(
+      id: id,
+      title: title,
+      fileName: platformFile.name,
+      filePath: '$id/$safeName', // 相对路径
+      fileExtension: extension,
+      createdAt: now,
+      updatedAt: now,
+    );
+
+    await provider.addReaderBook(readerBook);
+
+    if (context.mounted) {
+      ScaffoldMessenger.of(context).showSnackBar(
+        SnackBar(content: Text('「$title」导入成功')),
+      );
+    }
+
+    return readerBook;
+  }
+}