chore: improve Russian language support (#926)

## Summary

This PR includes vocabulary and grammar fixes for Russian translation,
originally made as review comments
[here](https://github.com/crosspoint-reader/crosspoint-reader/pull/728).

---

### AI Usage

While CrossPoint doesn't have restrictions on AI tools in contributing,
please be transparent about their usage as it
helps set the right context for reviewers.

Did you use AI tools to help write this code? _**NO**_

lib/I18n/translations/russian.yaml

@@ -109,7 +109,7 @@ STR_COLOR_MODE: "Цветовой режим"
 STR_SCREEN_MARGIN: "Поля экрана"
 STR_PARA_ALIGNMENT: "Выравнивание абзаца"
 STR_HYPHENATION: "Перенос слов"
-STR_TIME_TO_SLEEP: "Сон Через"
+STR_TIME_TO_SLEEP: "Сон через"
 STR_REFRESH_FREQ: "Частота обновления"
 STR_CALIBRE_SETTINGS: "Настройки Calibre"
 STR_KOREADER_SYNC: "Синхронизация KOReader"
@@ -164,9 +164,9 @@ STR_PORTRAIT: "Портрет"
 STR_LANDSCAPE_CW: "Ландшафт (CW)"
 STR_INVERTED: "Инверсия"
 STR_LANDSCAPE_CCW: "Ландшафт (CCW)"
-STR_FRONT_LAYOUT_BCLR: "Наз"
-STR_FRONT_LAYOUT_LRBC: "Лев"
-STR_FRONT_LAYOUT_LBCR: "Лев"
+STR_FRONT_LAYOUT_BCLR: "Наз, Ок, Лев, Прав"
+STR_FRONT_LAYOUT_LRBC: "Лев, Прав, Наз, Ок"
+STR_FRONT_LAYOUT_LBCR: "Лев, Наз, Ок, Прав"
 STR_PREV_NEXT: "Назад/Вперёд"
 STR_NEXT_PREV: "Вперёд/Назад"
 STR_BOOKERLY: "Bookerly"
@@ -203,7 +203,7 @@ STR_NO_UPDATE: "Обновлений нет"
 STR_UPDATE_FAILED: "Ошибка обновления"
 STR_UPDATE_COMPLETE: "Обновление завершено"
 STR_POWER_ON_HINT: "Удерживайте кнопку питания для включения"
-STR_EXTERNAL_FONT: "Внешний шрифт"
+STR_EXTERNAL_FONT: "Пользовательский шрифт"
 STR_BUILTIN_DISABLED: "Встроенный (отключён)"
 STR_NO_ENTRIES: "Записи не найдены"
 STR_DOWNLOADING: "Загрузка..."
@@ -246,7 +246,7 @@ STR_CAPS_ON: "CAPS"
 STR_CAPS_OFF: "caps"
 STR_OK_BUTTON: "OK"
 STR_ON_MARKER: "[ВКЛ]"
-STR_SLEEP_COVER_FILTER: "Фильтр обложки сна"
+STR_SLEEP_COVER_FILTER: "Фильтр экрана сна"
 STR_FILTER_CONTRAST: "Контраст"
 STR_STATUS_BAR_FULL_PERCENT: "Полная + %"
 STR_STATUS_BAR_FULL_BOOK: "Полная + шкала книги"