Clean up examples directory to essential demos only

- Remove 19 test/debug files to reduce clutter
- Keep only two focused examples:
  * ncdump.js: Command-line OpenDAP inspector (works on Node.js/Bun/Deno)
  * web-viewer.html: Clean web interface for viewing/downloading data
- Update web-viewer.html to use new ImmutableDataset API
- Examples now demonstrate core use cases without overwhelming users

🤖 Generated with [Claude Code](https://claude.ai/code)

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

Author: mpiannucci