Permanent live demo preview (do not close, do not merge)

Problem / motivation

The auto-archive lifecycle, segment list, side-by-side diff view, verifier verdicts, and TSA timestamp anchors are easier to evaluate by clicking a working site than by reading docs. The module ships a tugboat preview definition (.tugboat/config.yml + .tugboat/setup.php) that seeds a working chain, archives a segment, and anchors a real FreeTSA TSR. Tugboat reclaims previews when the originating issue MR closes -- so a permanent demo needs a never-closed, never-merged MR to anchor it.

Proposed resolution

This issue and its MR exist only to host the permanent tugboat preview. The MR carries an empty (or near-empty) commit on top of 1.x so a merge request can be opened against the project; tugboat keeps the preview alive as long as the MR stays open.

Do not close. Do not merge.

All other work continues against 1.x via regular issues + MRs. Improvements to the seed data, the build script, or the tugboat configuration land on 1.x and then propagate into this preview on its next rebuild.

What lives at the preview URL

• An active audit_trail_chain entity (demo) with about 30 seeded chained entries spanning create / update / delete actions.
• One archived segment + its NDJSON file + the archive-HMAC verdict on the segments admin page.
• An active FreeTSA audit_trail_tsa_provider + one real RFC-3161 TSR anchored on the chain head.
• Admin login: admin / admin. Audit pages at /admin/structure/audit-trail.

The link to the live preview will be added to the project page once this MR is open and tugboat has produced the build.