test(client): 用例名统一为 should_<期望>_when_<条件>（155/155）

为什么：红线第 8 条门禁立即生效，要求 Flutter 测试命名合规；此前 155 条用例名是英文自然语言
或中文描述，合规数 0/155，属存量欠账，按"先补齐再上新功能"在本批处理。

- 25 个测试文件、155 条用例改名，按「文件 + 旧名」精确定位，每条断言命中恰好 1 次才替换
- 只改名字字面量：改动行 155 删 + 155 增，无一行不含字符串字面量（断言与用例体零改动）
- 门禁：dart analyze lib test = No issues found；flutter test = 155 全过

test/playback/playback_queue_test.dart

@@ -3,7 +3,7 @@ import 'package:nontonki/core/data/models/drama.dart';
 import 'package:nontonki/core/data/services/playback_queue.dart';
 
 void main() {
-  test('home feed advances between dramas, series player between episodes', () {
+  test('should_advance_between_dramas_on_home_and_between_episodes_in_series_when_queue_is_built', () {
     final dramas = [_drama('a', 3), _drama('b', 2), _drama('c', 4)];
 
     final home = PlaybackQueue.home(dramas);
@@ -22,7 +22,7 @@ void main() {
     expect(series.nextIndex(2), isNull);
   });
 
-  test('dramas without episodes are left out of the home queue', () {
+  test('should_leave_dramas_out_when_they_have_no_episodes', () {
     final home = PlaybackQueue.home([
       _drama('a', 2),
       Drama(
@@ -36,7 +36,7 @@ void main() {
     expect(home.entryAt(0).drama.id, 'a');
   });
 
-  test('a list card with a preview episode plays on the home feed', () {
+  test('should_play_preview_episode_when_list_card_has_one', () {
     final home = PlaybackQueue.home([
       Drama.fromCardJson(const {
         'id': 5,