feat: 移植 B50 成绩图，并把项目名从 purarine 改回 ichino

海报从 Empurple 的 Best50ImageRenderer/ImageBuilder 移植：按原始像素坐标
(1762x1850 画布、300x100 卡片、5 列、行距 120) 叠加在 base.png 上，底图里
已画好的面板/药丸标签/页脚不重复绘制；页面外壳走 Ichino 的 Material 3。

RatingCalculator 的达成率分档改成单张有序表，避免偏移与评级错位；
RA 与评级由 test/rating_calculator_test.dart 的边界用例锁定。

GetUserRatingApi 只需要 userId(Cookie 可选)，所以 Preview API 模式、未登录
游戏服务器时也能出图，只是没有 FC/AP/FS 标记。导出用 RepaintBoundary 抓
全尺寸 PNG：原生走 share_plus(不支持文件分享的平台回退为落盘并提示路径)，
web 走下载。

BEST35 与 BEST15 改为各自独立排版。原先沿用 Empurple 的跨列表全局序号，
BEST35 没打满时 BEST15 会整体上移混进上半区。

path_provider 会经 path_provider_android 2.3.x 拖入 jni 插件，而 jni 把
windows/linux 也声明成 ffiPlugin，桌面构建因此去链接 jvm.lib 并失败，
故用 dependency_overrides 钉住 path_provider_android <2.3.0。

lib/services/music_data_cache.dart

@@ -0,0 +1,8 @@
+import 'music_data_cache_native.dart'
+    if (dart.library.html) 'music_data_cache_web.dart' as impl;
+
+/// 乐曲元数据的磁盘缓存，Web 平台为空实现。读失败返回 null，写失败静默忽略。
+Future<String?> readTextCache(String fileName) => impl.readTextCache(fileName);
+
+Future<void> writeTextCache(String fileName, String content) =>
+    impl.writeTextCache(fileName, content);

lib/services/music_data_cache_native.dart

@@ -0,0 +1,29 @@
+import 'dart:io';
+
+/// 乐曲元数据是可重新下载的参考数据，放系统临时目录即可，
+/// 不引入 path_provider（它经 path_provider_android 拖进 jni 插件，
+/// jni 会在 Windows 上强行链接 jvm.lib）。
+Future<String?> readTextCache(String fileName) async {
+  try {
+    final file = await _file(fileName);
+    if (!await file.exists()) return null;
+    final content = await file.readAsString();
+    return content.isEmpty ? null : content;
+  } catch (_) {
+    return null;
+  }
+}
+
+Future<void> writeTextCache(String fileName, String content) async {
+  try {
+    await (await _file(fileName)).writeAsString(content);
+  } catch (_) {
+    // 缓存是尽力而为，失败只影响下次启动的加载速度。
+  }
+}
+
+Future<File> _file(String fileName) async {
+  final dir = Directory('${Directory.systemTemp.path}/ichino_cache');
+  await dir.create(recursive: true);
+  return File('${dir.path}/$fileName');
+}

lib/services/music_data_cache_web.dart

@@ -0,0 +1,3 @@
+Future<String?> readTextCache(String fileName) async => null;
+
+Future<void> writeTextCache(String fileName, String content) async {}

lib/services/music_data_service.dart

@@ -0,0 +1,93 @@
+import 'dart:convert';
+
+import 'package:http/http.dart' as http;
+
+import 'music_data_cache.dart';
+
+class MusicInfo {
+  final String title;
+  final Map<int, double> dsByLevel;
+
+  const MusicInfo({required this.title, required this.dsByLevel});
+}
+
+/// 乐曲元数据来源，移植自 Empurple 的 `MusicDataProvider`。
+///
+/// 游戏接口的 ratingList 只有 musicId，曲名与各难度定数需要另行获取。
+class MusicDataService {
+  static const String _musicDataUrl =
+      'https://www.diving-fish.com/api/maimaidxprober/music_data';
+  static const String _cacheFileName = 'music_data.json';
+
+  MusicDataService._();
+
+  static final MusicDataService instance = MusicDataService._();
+
+  final Map<int, MusicInfo> _byId = {};
+  Future<void>? _inFlight;
+
+  String getTitle(int musicId) => _byId[musicId]?.title ?? 'Unknown';
+
+  /// 缺失定数时返回 0，RA 也随之为 0，与 Empurple 行为一致。
+  double getDs(int musicId, int level) =>
+      _byId[musicId]?.dsByLevel[level] ?? 0.0;
+
+  /// 并发调用共享同一次下载。
+  Future<void> load() {
+    if (_byId.isNotEmpty) return Future.value();
+    return _inFlight ??= _load().whenComplete(() => _inFlight = null);
+  }
+
+  Future<void> _load() async {
+    final cached = await readTextCache(_cacheFileName);
+    final content = cached ?? await _download();
+    _parse(content);
+    if (cached == null) {
+      await writeTextCache(_cacheFileName, content);
+    }
+  }
+
+  Future<String> _download() async {
+    final response = await http
+        .get(Uri.parse(_musicDataUrl), headers: const {'User-Agent': 'Ichino/1.0'})
+        .timeout(const Duration(seconds: 20));
+    if (response.statusCode != 200) {
+      throw Exception('music_data HTTP ${response.statusCode}');
+    }
+    return response.body;
+  }
+
+  void _parse(String content) {
+    final decoded = jsonDecode(content);
+    if (decoded is! List) return;
+    _byId.clear();
+    for (final item in decoded.whereType<Map<String, dynamic>>()) {
+      final id = _toInt(item['id']);
+      if (id == 0) continue;
+      final ds = item['ds'];
+      _byId[id] = MusicInfo(
+        title: item['title']?.toString() ?? 'Unknown',
+        dsByLevel: ds is List
+            ? {
+                for (var level = 0; level < ds.length; level++)
+                  level: _toDouble(ds[level]),
+              }
+            : const {},
+      );
+    }
+  }
+
+  static int _toInt(dynamic v) {
+    if (v is int) return v;
+    if (v is num) return v.toInt();
+    if (v is String) return int.tryParse(v) ?? 0;
+    return 0;
+  }
+
+  static double _toDouble(dynamic v) {
+    if (v is double) return v;
+    if (v is int) return v.toDouble();
+    if (v is String) return double.tryParse(v) ?? 0.0;
+    return 0.0;
+  }
+}

lib/services/png_export_service.dart

@@ -0,0 +1,10 @@
+import 'dart:typed_data';
+
+import 'png_export_service_native.dart'
+    if (dart.library.html) 'png_export_service_web.dart' as impl;
+
+/// 导出一张 PNG：原生平台落临时盘并拉起系统分享，Web 走下载或 Web Share API。
+///
+/// 返回原生平台上的落盘路径（用于分享能力缺失时提示用户），Web 返回 null。
+Future<String?> exportPng(Uint8List bytes, String fileName) =>
+    impl.exportPng(bytes, fileName);

lib/services/png_export_service_native.dart

@@ -0,0 +1,22 @@
+import 'dart:io';
+import 'dart:typed_data';
+
+import 'package:share_plus/share_plus.dart';
+
+Future<String?> exportPng(Uint8List bytes, String fileName) async {
+  final file = File('${Directory.systemTemp.path}/$fileName');
+  await file.writeAsBytes(bytes);
+
+  try {
+    await SharePlus.instance.share(
+      ShareParams(
+        files: [XFile.fromData(bytes, name: fileName, mimeType: 'image/png')],
+        fileNameOverrides: [fileName],
+      ),
+    );
+  } on UnimplementedError {
+    // Linux 与 Windows 10 RS5 之前不支持分享文件，文件已落盘，返回路径即可。
+  }
+
+  return file.path;
+}

lib/services/png_export_service_web.dart

@@ -0,0 +1,15 @@
+import 'dart:typed_data';
+
+import 'package:share_plus/share_plus.dart';
+
+Future<String?> exportPng(Uint8List bytes, String fileName) async {
+  await SharePlus.instance.share(
+    ShareParams(
+      files: [
+        XFile.fromData(bytes, name: fileName, mimeType: 'image/png'),
+      ],
+      fileNameOverrides: [fileName],
+    ),
+  );
+  return null;
+}

lib/services/qr_service_native.dart

@@ -1,6 +1,6 @@
 import 'package:flutter/services.dart';
 
-const _channel = MethodChannel('dev.naominet.purarine/qr_scanner');
+const _channel = MethodChannel('dev.naominet.ichino/qr_scanner');
 
 Future<String?> decodeQRFromBytes(Uint8List bytes) async {
   try {

lib/services/rating_calculator.dart

@@ -0,0 +1,65 @@
+/// RA / 评级计算，移植自 Empurple 的 `RatingCalculator`。
+///
+/// `achievement` 传入百分比数值（接口原值 1001234 => 100.1234），`ds` 为谱面定数。
+class RaResult {
+  final int ra;
+  final String rate;
+
+  const RaResult(this.ra, this.rate);
+}
+
+/// 达成率区间上界 / RA 系数 / 评级，顺序与 Empurple 的 when 分支一致。
+const List<(int, int, String)> _bands = [
+  (100000, 0, 'D'),
+  (200000, 16, 'D'),
+  (300000, 32, 'D'),
+  (400000, 48, 'D'),
+  (500000, 64, 'D'),
+  (600000, 80, 'C'),
+  (700000, 96, 'B'),
+  (750000, 112, 'BB'),
+  (799999, 120, 'BBB'),
+  (800000, 128, 'BBB'),
+  (900000, 136, 'A'),
+  (940000, 152, 'AA'),
+  (969999, 168, 'AAA'),
+  (970000, 176, 'AAA'),
+  (980000, 200, 'S'),
+  (989999, 203, 'Sp'),
+  (990000, 206, 'Sp'),
+  (995000, 208, 'SS'),
+  (999999, 211, 'SSp'),
+  (1000000, 214, 'SSp'),
+  (1004999, 216, 'SSS'),
+  (1005000, 222, 'SSS'),
+];
+
+const int _maxAchievement = 1005000;
+const int _ssspOffset = 224;
+
+class RatingCalculator {
+  RatingCalculator._();
+
+  static int computeRa(double ds, double achievement) =>
+      compute(ds, achievement).ra;
+
+  static String computeRaRate(double ds, double achievement) =>
+      compute(ds, achievement).rate;
+
+  static RaResult compute(double ds, double achievement) {
+    final achievementRaw =
+        (achievement * 10000.0).round().clamp(0, _maxAchievement);
+    var offset = _ssspOffset;
+    var rate = 'SSSp';
+    for (final (upperBound, bandOffset, bandRate) in _bands) {
+      if (achievementRaw < upperBound) {
+        offset = bandOffset;
+        rate = bandRate;
+        break;
+      }
+    }
+    final scoreRate = (ds * 10.0).round();
+    final ra = scoreRate * achievementRaw * offset ~/ 100000000;
+    return RaResult(ra, rate);
+  }
+}

lib/services/title_api_service.dart

@@ -10,6 +10,7 @@ import 'package:pointycastle/export.dart';
 import '../config/title_server_config.dart';
 import '../models/user_data.dart';
 import '../models/user_preview.dart';
+import '../models/user_rating.dart';
 
 class TitleApiException implements Exception {
   final String message;
@@ -354,6 +355,11 @@ class TitleApiService {
     return _callApi('GetUserRatingApi', {'userId': userId}, userId);
   }
 
+  Future<UserRatingBean> getUserRatingTyped(int userId) async {
+    final json = await getUserRating(userId);
+    return UserRatingBean.fromJson(json);
+  }
+
   Future<Map<String, dynamic>> getUserCharge(int userId) async {
     return _callApi('GetUserChargeApi', {'userId': userId}, userId);
   }