fix: localize sleep overlay strings, validate TXT cache header, migrate overlay enum

lib/I18n/I18nKeys.h

@@ -351,6 +351,9 @@ enum class StrId : uint16_t {
   STR_OVERLAY_GRAY,
   STR_OVERLAY_BLACK,
   STR_OVERLAY_OFF,
+  STR_OVERLAY_READING_PROGRESS,
+  STR_OVERLAY_READING_PROGRESS_NO_TOTAL,
+  STR_OVERLAY_CHAPTER_PAGE_SUFFIX,
   // Sentinel - must be last
   _COUNT
 };
@@ -405,8 +408,7 @@ inline const char* const* getStringArray(Language lang) {
 constexpr uint8_t getLanguageCount() { return static_cast<uint8_t>(Language::_COUNT); }
 
 // Sorted language indices by code (auto-generated by gen_i18n.py)
-// Order: English, Беларуская, Català, Čeština, Dansk, Deutsch, Español, Suomi, Français, Italiano, Қазақша, Nederlands,
-// Polski, Português (Brasil), Română, Русский, Svenska, Türkçe, Українська
+// Order: English, Беларуская, Català, Čeština, Dansk, Deutsch, Español, Suomi, Français, Italiano, Қазақша, Nederlands, Polski, Português (Brasil), Română, Русский, Svenska, Türkçe, Українська
 constexpr uint8_t SORTED_LANGUAGE_INDICES[] = {0, 11, 9, 4, 15, 3, 1, 14, 2, 12, 18, 16, 13, 5, 8, 6, 7, 17, 10};
 
 static_assert(sizeof(SORTED_LANGUAGE_INDICES) / sizeof(SORTED_LANGUAGE_INDICES[0]) == getLanguageCount(),