Translate missing Simplified Chinese live-chat widget availability and
reply-time strings so visitors using `zh_CN` no longer see English
fallbacks in offline and pre-chat states.
## Closes
N/A
## How to test
- Open the widget with `Widget Locale = 中文 (zh_CN)` and set the team
offline. The availability card should stay in Chinese.
- Configure working hours so the widget shows minute, hour, tomorrow,
and day-specific return states. The `{time}`, `{n}`, and `{day}`
placeholders should render correctly.
## What changed
- Translated missing `THUMBNAIL.AUTHOR.NOT_AVAILABLE`,
`TEAM_AVAILABILITY.BACK_AS_SOON_AS_POSSIBLE`, and `REPLY_TIME.*` strings
in `app/javascript/widget/i18n/locale/zh_CN.json`.
- Kept the scope limited to Simplified Chinese.
Co-authored-by: Sojan Jose <sojan@pepalo.com>
