v1.52.0 — the demo page kept current

The demo page kept current. DOCUMENTATION.md has said since 1.47.0 that a
demo still showing old behavior is an incomplete change, but the rule lived
only there — the workflow steps and checklists agents actually follow never
mentioned demo.html, so nothing prompted the update. This release puts it
where agents look.

Changed

• Agents are told to keep the demo page current. DOCUMENTATION.md
  already said a demo still showing old behavior is an incomplete change, but
  nothing an agent works from said so. Now AI_WORKFLOW.md Required Workflow
  step 20 and "Before Completing Work", every agent instruction file and
  template, the Solon reviewer, and both pull request templates carry the
  rule: when a change alters user-facing behavior and the repository has a
  demo.html, update it in the same change. tests.yml enforces the rule
  across instruction files with a demo page current anchor; the checker's
  default anchors are unchanged, so no adopter's strict run changes behavior.