chore: clean up unused files and legacy template assets

- Remove build.sh (no longer needed without Less preprocessing)
- Remove .vscode/ (IDE config not needed in repo)
- Remove empty _includes/ directory
- Delete 104 unused images from original Hux Blog template:
  - Backup files (*.bak)
  - Original author avatar (avatar-hux.jpg)
  - WeChat icon (icon_wechat.png)
  - Demo images (blog-desktop, blog-keynote, etc.)
  - Unused post backgrounds (23 files)
  - Unused in-post directories (alitrip, eleme-pwa, js-version, nextgen-web-pwa, wmu)

Preserved: .claude/, essential images (favicon, avatar-jason, 404-bg, home-bg, post-bg-2015, post-bg-web)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: calderbuild