feat(i18n): add missing zh-Hans translations (#15032)

## Summary

This PR completes the missing Simplified Chinese (`zh-Hans`) i18n
resource coverage.

The current i18n completeness calculation is based on key coverage
between `en.json` and each locale resource file. Before this change,
`zh-Hans.json` contained 2331 keys while `en.json` contained 2406 keys,
resulting in a displayed completeness of 97%.

This change adds the 75 missing `zh-Hans` translation entries and
updates the generated completeness value for `zh-Hans` from 97% to 100%.

## Changes

- Added 75 missing Simplified Chinese translations to
`packages/frontend/i18n/src/resources/zh-Hans.json`.
- Updated `packages/frontend/i18n/src/i18n-completenesses.json` so
`zh-Hans` now reports 100% completeness.
- Kept the scope limited to missing i18n resource keys only.

## Notes

This PR does not modify existing `zh-Hans` translations, terminology
choices, or hardcoded English UI strings outside the i18n resource
files.

## Verification

- Confirmed `zh-Hans.json` parses successfully.
- Confirmed `zh-Hans.json` now has full key coverage against `en.json`.
- Confirmed missing key count is 0.
- Confirmed computed `zh-Hans` completeness is 100%.
- Ran pre-commit checks:
  - `yarn lint-staged`
  - `yarn lint:ox`

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## Summary by CodeRabbit

* **Chores**
* Completed Chinese (Simplified) translations with 100% coverage for the
application.
* Added new translations across multiple areas: appearance and image
settings, export functionality, document import from Bear and Obsidian,
analytics and viewer information, editor settings including auto-date
titles and icon options, workspace sharing controls, calendar
integration with CalDAV support, share menu tooltips, and comprehensive
error messages.

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