What this PR does / why we need it:
Converts 252 PNG images in website/ to WebP format, reducing repository
size by ~100MB (~70%). Also adds two reusable scripts for future asset
optimization and updates all markdown/vue references accordingly.

JPG/JPEG photos are intentionally kept unchanged — re-compressing them
causes visible quality loss.

Which issue(s) this PR fixes:
Fixes #

Special notes for your reviewer:
Some PNG files in the repository are photographs saved as PNG instead of JPG
(e.g. hackathon group pictures like 2025-07.png, 2025-06.png). After
converting to WebP at quality 85, these appear slightly washed out compared
to the originals.

Please advise on preferred approach:

1. Accept current quality (still ~70% smaller)
2. Increase quality to 90-92 (less savings)
3. Exclude hackathon group pictures from conversion

Summary by CodeRabbit

Release Notes

• New Features

  • Added WebP image format support across the project
  • Introduced asset optimization tooling that converts PNG images to WebP format, reducing file sizes while automatically updating all references

• Chores

  • Added image processing library to development dependencies