* feat(lang): add Greek & Polish display languages
Also:
* rename zh-TW display language to 繁體中文
* fix plurality of AvailableLocale type name
* consistently use 'en' as fallback/default language
* revert(lang): remove Polish display language due to lack of translation activity
* refactor(ui): add tabs to user notification settings
* feat(notif): allow users to enable/disable specific agents
* fix(ui): only enforce required fields when agent is enabled
* fix(ui): hide unavailable notification agents
* feat(notif): mention admin users for admin Discord notifications
* fix(ui): modify styling of PGP key textareas to suit expected input
* fix(notif): mention all admins when there are multiple and fix rebase error
* fix: add missing form values, and fix Yup validation
* refactor: reduce repeated logic/code in email notif agent
* refactor: move 'Notification Types' label into NotificationTypeSelector component
* fix(email): correct inconsistencies in email template formatting
* refactor: use bitfields for storing user-enabled notif agent types
* feat: improve notification agent logging
* fix(ui): mark string fields as nullable so empty values are not type errors
* fix: add validation for PGP-related inputs
* fix: correctly fetch user in user settings & log mentioned IDs for Discord notifs
* fix(ui): fix mobile nav dropdown text & add hover effect to button-style tabs
* fix(notif): process admin email notifications asynchronously
* fix(logging): log name of notification type instead of its enum value
* fix: mark required fields and pass all user settings values to API
* fix(frontend): call mutate after changing email/Discord/Telegram global notif settings
* refactor: get global notif settings from relevant API endpoints instead of adding to public settings
* fix(notif): fall back to email notifications being enabled (default) if user settings do not exist
* fix(notif): do not set notifyUser for MEDIA_PENDING or MEDIA_AUTO_APPROVED
* fix: expose notif enabled settings in user notif endpoints & remove global enable notif setting
* fix(notif): remove unnecessary allowed_mentions object from Discord payload
* fix(notif): use form values for email test notification
* fix: make suggested changes and regenerate DB migration
* fix: loosen validation of PGP keys
* fix: fix user profile settings routes
* fix: remove route guard from profile pages
* feat(ui): add user requests page
* fix: return error if user attempts to fetch another user's requests without adequate perms
* fix(ui): make user name on request page link back to user profile
* feat(ui): link user request count to their filtered request list view
* fix(frontend): only display user requests on profiles if current user has adequate perms
* fix: use 'all' filter for user-filtered request list
* fix(frontend): pass userId to router.push()
* fix: do not pass userId in query for non-user-filtered requests page
* fix(frontend): also allow REQUEST_VIEW perm through route guard
* fix(frontend): only link request count to user request list if current user has required perms
