feat: add regenerate all previews functionality and update localization strings

qwen3-tts-frontend/src/locales/en-US/audiobook.json

@@ -85,7 +85,12 @@
       "voiceDesign": "Voice #{{id}}",
       "noVoice": "Unassigned",
       "editTitle": "Edit Character: {{name}}",
-      "savedSuccess": "Character saved"
+      "savedSuccess": "Character saved",
+      "regeneratingPreview": "Regenerating...",
+      "regeneratePreview": "Regenerate Preview",
+      "regenerateAll": "Regenerate All Previews",
+      "regenerateAllDone": "All previews regenerated",
+      "previewNotReady": "Collecting preview..."
     },
 
     "confirm": {

qwen3-tts-frontend/src/locales/ja-JP/audiobook.json

@@ -84,7 +84,12 @@
       "voiceDesign": "音声 #{{id}}",
       "noVoice": "未割り当て",
       "editTitle": "キャラクターを編集：{{name}}",
-      "savedSuccess": "キャラクターを保存しました"
+      "savedSuccess": "キャラクターを保存しました",
+      "regeneratingPreview": "試聴を再生成中...",
+      "regeneratePreview": "試聴を再生成",
+      "regenerateAll": "試聴を一括再生成",
+      "regenerateAllDone": "すべての試聴を再生成しました",
+      "previewNotReady": "試聴を収集中..."
     },
 
     "confirm": {

qwen3-tts-frontend/src/locales/ko-KR/audiobook.json

@@ -84,7 +84,12 @@
       "voiceDesign": "음성 #{{id}}",
       "noVoice": "미할당",
       "editTitle": "캐릭터 편집: {{name}}",
-      "savedSuccess": "캐릭터가 저장되었습니다"
+      "savedSuccess": "캐릭터가 저장되었습니다",
+      "regeneratingPreview": "미리듣기 재생성 중...",
+      "regeneratePreview": "미리듣기 재생성",
+      "regenerateAll": "미리듣기 일괄 재생성",
+      "regenerateAllDone": "모든 미리듣기가 재생성되었습니다",
+      "previewNotReady": "미리듣기 수집 중..."
     },
 
     "confirm": {

qwen3-tts-frontend/src/locales/zh-CN/audiobook.json

@@ -88,6 +88,8 @@
       "savedSuccess": "角色已保存",
       "regeneratingPreview": "重新生成试听中...",
       "regeneratePreview": "重生试听",
+      "regenerateAll": "一键重新生成试听",
+      "regenerateAllDone": "所有试听已重新生成",
       "previewNotReady": "试听收集中..."
     },
 

qwen3-tts-frontend/src/locales/zh-TW/audiobook.json

@@ -84,7 +84,12 @@
       "voiceDesign": "音色 #{{id}}",
       "noVoice": "未分配",
       "editTitle": "編輯角色：{{name}}",
-      "savedSuccess": "角色已儲存"
+      "savedSuccess": "角色已儲存",
+      "regeneratingPreview": "重新生成試聽中...",
+      "regeneratePreview": "重生試聽",
+      "regenerateAll": "一鍵重新生成試聽",
+      "regenerateAllDone": "所有試聽已重新生成",
+      "previewNotReady": "試聽收集中..."
     },
 
     "confirm": {