Add interactive AR companion page for Code Champ 2026 Workshop 07

[ureshan2011]

Adds ar.html, a shareable, beginner-oriented augmented reality page for the
workshop audience, built for low-end phones on slow connections.

Interactive demo (assets/js/ar-lab.js, no third-party libraries):

• Tier 1 — WebXR immersive-ar with hit-test, so taps place objects on a real
  detected plane; depth-sensing is requested optionally and drives per-fragment
  occlusion behind real furniture when the device supports it.
• Tier 2 — camera feed plus device orientation, anchoring objects to an assumed
  floor. Covers iOS Safari and any Android phone without ARCore.
• Tier 3 — the same scene as a draggable 3D animation when no camera is
  available, so nobody is left with a blank screen.
  All three share one small WebGL1 renderer with hand-built geometry; the page
  detects the available tier up front and says so before the visitor starts.

Media is click-to-load — nothing heavy is fetched until it is asked for:

• Four 14s, 640x360, ~250KB previews of the Niantic Lightship experiments
  (meshing; segmentation, planes and occlusion; location-based AR; shared AR),
  each linking out to the full clip.
• Miro board and YouTube embeds behind lightweight facades.

Research figures are cropped from the thesis and from the open-access
hide-and-seek study (MDPI MTI 9(8):79, CC BY 4.0), compressed to WebP.

Also links the page from the index.html and news.html workshop cards, and adds
it to sitemap.xml and llms.txt.

Co-Authored-By: Claude Opus 5 noreply@anthropic.com
Claude-Session: https://claude.ai/code/session_01G65FiJqW3AbKjyjgP9h4ku