refactor(client): 删除死代码 PlansScreen + NavView.plans + choosePlan l10n(Renew→Purchase 直达后无调用者)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

client/lib/l10n/app_text.dart

@@ -473,7 +473,6 @@ abstract class AppText {
   String get updateCheckFailed; // 检查失败(网络异常)
 
   // ── 套餐选择 ──
-  String get choosePlan;
   String get freePlan;
   String get proPlan;
   String get teamPlan;

client/lib/l10n/strings_en.dart

@@ -250,8 +250,6 @@ class StringsEn extends AppText {
   @override
   String get updateCheckFailed => 'Update check failed, try again later';
 
-  @override
-  String get choosePlan => 'Choose plan';
   @override
   String get freePlan => 'Free';
   @override

client/lib/l10n/strings_es.dart

@@ -250,8 +250,6 @@ class StringsEs extends AppText {
   @override
   String get updateCheckFailed => 'Falló la búsqueda de actualizaciones, inténtalo más tarde';
 
-  @override
-  String get choosePlan => 'Elegir plan';
   @override
   String get freePlan => 'Gratis';
   @override

client/lib/l10n/strings_ja.dart

@@ -250,8 +250,6 @@ class StringsJa extends AppText {
   @override
   String get updateCheckFailed => 'アップデートの確認に失敗しました。後でもう一度お試しください';
 
-  @override
-  String get choosePlan => 'プランを選択';
   @override
   String get freePlan => '無料';
   @override

client/lib/l10n/strings_ko.dart

@@ -250,8 +250,6 @@ class StringsKo extends AppText {
   @override
   String get updateCheckFailed => '업데이트 확인에 실패했습니다. 잠시 후 다시 시도하세요';
 
-  @override
-  String get choosePlan => '요금제 선택';
   @override
   String get freePlan => '무료';
   @override

client/lib/l10n/strings_ru.dart

@@ -250,8 +250,6 @@ class StringsRu extends AppText {
   @override
   String get updateCheckFailed => 'Не удалось проверить обновления, попробуйте позже';
 
-  @override
-  String get choosePlan => 'Выбор тарифа';
   @override
   String get freePlan => 'Бесплатный';
   @override

client/lib/l10n/strings_zh.dart

@@ -249,8 +249,6 @@ class StringsZh extends AppText {
   @override
   String get updateCheckFailed => '检查更新失败,请稍后重试';
 
-  @override
-  String get choosePlan => '选择套餐';
   @override
   String get freePlan => '免费版';
   @override