fix(client): 兼容后端 Long 字段字符串化（id 与计数）

后端 J1 起 Long/long 一律以字符串下发（含雪花 id 与 viewCount/expiresIn）。
客户端 id 方向本来就是 (json['id'] ?? '').toString()，不受影响；会被 as num? 打挂的
是 Long 计数，这里加统一兼容解析并替换 3 处：

- lib/core/data/models/json_numbers.dart（新增，接受数字或数字字符串）
- lib/core/data/models/auth_session.dart（expiresIn，后端 long）
- lib/core/data/models/drama.dart（viewCount，后端 Long ×2）
- test/core/json_id_parsing_test.dart（新增 8 条回归用例）

其余 as num?（durationSec/unlockCoin/number/totalEpisodes/freeEpisodes/code）对应后端
Integer/int，仍是数字，未改动；未碰任何业务逻辑与 UI。

test/core/json_id_parsing_test.dart

@@ -0,0 +1,103 @@
+// Author: fruit.com.cn
+
+import 'package:flutter_test/flutter_test.dart';
+import 'package:fruitshorts/core/data/models/auth_session.dart';
+import 'package:fruitshorts/core/data/models/drama.dart';
+import 'package:fruitshorts/core/data/models/json_numbers.dart';
+import 'package:fruitshorts/core/data/models/play_ticket.dart';
+
+/// 后端契约（FruitServer/docs/api-phase1.md §0）：`Long`/`long` 字段以字符串下发。
+/// 这里钉住客户端在"收到字符串形式的 id / 计数"时照样能解析，不抛异常。
+void main() {
+  group('jsonToInt', () {
+    test('should_parse_int_when_value_is_number', () {
+      expect(jsonToInt(12345), 12345);
+      expect(jsonToInt(12.9), 12);
+    });
+
+    test('should_parse_int_when_value_is_numeric_string', () {
+      expect(jsonToInt('2111012753262120962'), 2111012753262120962);
+      expect(jsonToInt(' 42 '), 42);
+    });
+
+    test('should_fall_back_when_value_is_missing_or_invalid', () {
+      expect(jsonToInt(null), 0);
+      expect(jsonToInt(''), 0);
+      expect(jsonToInt('abc'), 0);
+      expect(jsonToInt(null, fallback: 7), 7);
+    });
+  });
+
+  group('drama model', () {
+    test('should_parse_string_ids_when_backend_sends_ids_as_string', () {
+      final drama = Drama.fromCardJson({
+        'id': '2111012753262120962',
+        'title': '闪婚后，傅先生每天都在撒糖',
+        'totalEpisodes': 72,
+        'viewCount': '3100000',
+        'isHot': true,
+      });
+
+      expect(drama.id, '2111012753262120962');
+      expect(drama.title, '闪婚后，傅先生每天都在撒糖');
+      expect(drama.totalEpisodes, 72);
+      // viewCount 后端是 Long → 字符串
+      expect(drama.viewCount, 3100000);
+    });
+
+    test('should_parse_view_count_when_backend_sends_number', () {
+      final drama = Drama.fromCardJson({'id': 5, 'title': 'T', 'viewCount': 1200});
+
+      expect(drama.id, '5');
+      expect(drama.viewCount, 1200);
+    });
+
+    test('should_parse_detail_payload_when_ids_are_strings', () {
+      final drama = Drama.fromDetailJson({
+        'id': '2111012753262120962',
+        'title': 'T',
+        'totalEpisodes': 12,
+        'freeEpisodes': 3,
+        'viewCount': '99',
+        'episodes': [
+          {'id': '2111012753262120963', 'number': 1, 'title': 'E1', 'isFree': true},
+        ],
+      });
+
+      expect(drama.id, '2111012753262120962');
+      expect(drama.freeEpisodes, 3);
+      expect(drama.viewCount, 99);
+      expect(drama.episodes.first.id, '2111012753262120963');
+      expect(drama.episodes.first.number, 1);
+    });
+  });
+
+  group('auth session', () {
+    test('should_parse_expires_in_when_backend_sends_string', () {
+      final session = AuthSession.fromJson({
+        'accessToken': 'a',
+        'refreshToken': 'r',
+        'expiresIn': '7200',
+        'user': {'uid': 'u-1', 'nickname': 'n'},
+      });
+
+      expect(session.expiresIn, 7200);
+      expect(session.user.uid, 'u-1');
+    });
+  });
+
+  group('play ticket', () {
+    test('should_parse_episode_id_when_backend_sends_string', () {
+      final ticket = PlayTicket.fromJson({
+        'episodeId': '2111012753262120963',
+        'accessible': false,
+        'accessType': PlayTicket.coinRequired,
+        'unlockCoin': 30,
+      });
+
+      expect(ticket.episodeId, '2111012753262120963');
+      expect(ticket.unlockCoin, 30);
+      expect(ticket.needsUnlock, isTrue);
+    });
+  });
+}