Update Dockerfile demo-image URL to the renamed GitHub repo

Classroom Monitoring overhaul + Attendance UI updates (see SESSION_SUMMARY.md)

Retrigger build: demo_classroom.jpg now resolves on origin's raw URL

Switch attendance recognition backbone from glintr100 to AdaFace IR-101

Bake demo image into Docker image via GitHub raw URL

Add Preview demo image button alongside Run demo button

PRISM AI — with demo attendance button