feat: implement account switcher component and state management

- Add AccountSwitcher component for managing user accounts with UI for switching, adding, and logging out.
- Create account state manager to handle snapshots of account-specific states for efficient switching.
- Introduce utility functions for account management, including ID generation and avatar color assignment.
- Implement Zustand store for account management, supporting addition, removal, and state retrieval of accounts.

locales/ja/common.json

@@ -34,6 +34,9 @@
     "dismiss": "閉じる",
     "or": "または",
     "sign_in_sso": "SSOでサインイン",
+    "add_account_title": "アカウントを追加",
+    "add_account_subtitle": "別のアカウントでサインイン",
+    "cancel": "キャンセル",
     "website": "ウェブサイト",
     "imprint": "サイト運営者情報",
     "privacy_policy": "プライバシーポリシー",
@@ -58,6 +61,11 @@
     "storage_free": "空き",
     "storage_total": "合計",
     "sign_out": "サインアウト",
+    "sign_out_of": "{account} からサインアウト",
+    "sign_out_all": "すべてのアカウントからサインアウト",
+    "add_account": "アカウントを追加",
+    "set_as_default": "デフォルトに設定",
+    "switch_account": "アカウントを切り替え",
     "contacts": "連絡先",
     "calendar": "カレンダー",
     "settings": "設定",