The root .gitignore had a blanket `package-lock.json` rule that prevented
the docs lock file from being committed. Change it to `/package-lock.json`
(root-only) and commit the generated lock file so `npm ci` and
setup-node cache work in the docs workflow.
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