feat: refactor email tagging system to use labels instead of colors

- Updated EmailContextMenu to replace color tag functionality with label tags.
- Modified EmailListItem to display label badges for emails based on keywords.
- Enhanced EmailViewer to include a tag picker for emails.
- Adjusted ThreadListItem to show label badges for email subjects.
- Added tests for email list item and keyword settings to ensure proper functionality of the new tagging system.
- Updated localization files to reflect changes from color tags to labels in multiple languages.

locales/ja/common.json

@@ -155,9 +155,10 @@
     "back_to_list": "リストに戻る",
     "message_details": "メッセージの詳細",
     "more_reply_options": "その他の返信オプション",
-    "set_color": "色を設定",
+    "set_color": "ラベルを設定",
+    "tag": "ラベル",
     "more_actions": "その他の操作",
-    "remove_color": "色を削除",
+    "remove_color": "ラベルを削除",
     "more_count": "他{count}件",
     "characters_count": "{count}文字",
     "quick_reply_placeholder": "クイック返信を入力...",
@@ -929,8 +930,8 @@
     "delete": "削除",
     "mark_as_spam": "迷惑メールを報告",
     "not_spam": "迷惑メールでない",
-    "color_tag": "カラータグ",
-    "remove_color": "色を削除",
+    "color_tag": "ラベル",
+    "remove_color": "ラベルを削除",
     "items_selected": "{count}件のメールを選択"
   },
   "shortcuts": {