Close #330 and activate #316

[MajorIncident]

Purpose

Reconcile durable Classroom/cold-start documentation after the successful #330 / PR #334 merge and production publication.

Verified closeout

• Startup experience hub with explicit resume and new-session choices #330 merged via PR Add explicit startup experience hub #334 as ad7b9835adf3fd5338658f29b634e18b13b2def5.
• Exact PR head passed CI, CodeQL, Dependency Review, and Template Manifest Guard.
• Merged main deployment dpl_Er3Paodujp4g7WynCzAAHxdy1mLn reached Vercel production READY.
• Runtime scan shows no new application failure from Startup experience hub with explicit resume and new-session choices #330; the only reported item is the pre-existing Node url.parse() deprecation warning on /api/classroom.

Documentation changes

• mark Startup experience hub with explicit resume and new-session choices #330 complete/published;
• mark Classroom follow-on: Protected staged case assets and rich Student case rendering #316 as the active next implementation slice;
• preserve Classroom follow-on: Author and validate the first production staged KT Case Study #317 as dependent on Classroom follow-on: Protected staged case assets and rich Student case rendering #316;
• update the cold-start handoff so a new contributor does not resume the already-completed startup hub.

Next action

After this documentation-only PR is green/merged, begin #316 protected staged assets and rich Student case rendering from fresh main.