feat(i18n): standardize English and Simplified Chinese localization across UI

feat(i18n): standardize English and Simplified Chinese UI strings

- Move hardcoded user-facing text from Compose screens and dialogs into string resources
- Add and refine English and zh-rCN translations for settings, theme, about, backup, TOC, and book info flows
- Keep internal logs, exceptions, parser text, and comments unchanged unless user-facing
- Preserve existing behavior while improving localization consistency

.gitignore

@@ -17,3 +17,4 @@ package-lock.json
 # Kotlin 2.0
 .kotlin/
 /.vscode/settings.json
+/.codex/skills