feat(a11y): form input labels (H-6), remaining button labels (C-1)

H-6: aria-label on all form inputs missing accessible names:
  - Login: username, password (already done)
  - Register: username, password, confirm, token, email
  - Password reset: email, new password, confirm password
  - Settings: display name, user ID to ignore, keyword, page zoom,
    date format, device name, backup passwords (new/confirm/restore)
  - Auth: server URL picker input
C-1: additional icon buttons:
  - RoomInput: toolbar toggle (aria-pressed + label)
  - Lobby/Members: scroll to top, toggle member list
  - UIAFlowOverlay: cancel authentication
  - BackupRestore: backup options menu
  - UrlPreview: previous/next preview buttons
  - RoomPacks: undo remove/remove pack buttons
  - RoomViewHeader: start call, member list toggle
  - ServerPicker: change server button

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/app/features/settings/notifications/KeywordMessages.tsx

@@ -65,6 +65,7 @@ function KeywordInput() {
         <Input
           required
           name="keywordInput"
+          aria-label="Notification keyword"
           value={keyword}
           onChange={handleChange}
           variant="Secondary"