Consolidate the public chamber surface

[XyraSinclair]

Intent

Make the repository substantially easier to inspect and trust.

This pass will:

• draw a hard boundary between the maintained public system and historical or exploratory work;
• collapse duplicated verifier and packaging logic where behavior is already shared;
• replace the oversized single-file demo surface with a legible package boundary without changing its contracts;
• tighten the front doors so claims, assurance, runnable entry points, and limitations are visible immediately;
• preserve compatibility and prove the restructuring with the existing test and conformance surfaces.

The current workflow-only commit exists to make a credential-free checkout available for the refactor. It will be removed before review.