refactor(settings): drop Safety and the classifier rollback, collapse the Access tree

Safety held one thing: rolling back the AI classification tag assignments. The
classifier is gone, so the panel had nothing left to be about and the section is
removed, along with the snapshot state and the rollback call that fed it.
Permissions — the other thing that section might have grown into — already have
a page in Access.

"Search and sign-up" carried two controls that live somewhere else: a Public
Registration toggle that Access and joining already owns, and an embedding model
field that belongs with the other models. The duplicate registration toggle is
gone and the section is now just Search.

The account menu no longer offers Administration. It pointed at /settings?s=people
— the same page the Settings entry above it opens — so it was two names for one
door. Settings already shows the site sections to an administrator.

Access: the branch tree opened its top level by default and ran to hundreds of
rows, which buried the image libraries below it. Every branch now starts closed,
opening one closes the one before it at the same depth, and the tree scrolls
inside a bounded box. Picking a different person collapses it again. A "Clear all
access" control removes every grant a person holds, including the everything
role, for starting over.

The standfirst is reworded to lead with what to do rather than with a definition.

Tests updated rather than worked around: the Settings test asserted Safety was a
section, and the Access test reached a child branch that is no longer open on
load. Both now assert the new behaviour, plus two new cases — that branches start
collapsed, and that opening one closes the previous. 346 frontend tests pass.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Dv6sqaY6Vq3ChZHMem3cnU