docs(themes): add Lostar theme entry

[kasuganodesu]

Check List

• I want to publish my theme on Hexo official website.
  • I have read the theme publishing doc.
  • name is unique.
  • link URL is correct.
  • preview URL is correct.
  • preview URL web site is rendered correctly.
  • Add a screenshot to source/themes/screenshots.
  • Screenshot filename is same as value of name.
  • Screenshot size is 800 * 500.
  • Screenshot file format is png.

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Add Hexo theme listing entry for Lostar.

Changes

• Add source/_data/themes/lostar.yml
• Add source/themes/screenshots/lostar.png (800x500 PNG)
• Set preview URL to live demo: https://lostar.thatnghiep.dev

Theme repository

• https://github.com/thatnghiep-dev/hexo-theme-lostar

Demo

• https://lostar.thatnghiep.dev

[github-actions]

✅ Theme thumbnails validation completed.

[kasuganodesu]

Thanks for the CI signal. I added the required screenshot file: (800x500 PNG). This should resolve the thumbnail validation failure.