fix: TeamManager admin rules, close role self-escalation, escalate-only resync (#27)

TeamManager could not manage the roster: updateRule allowed self-update
only and deleteRule was superuser-only. The same self-update rule also
left a privilege escalation open — it did not restrict fields, so any
authenticated user could PATCH their own role to "admin".

- team_members rules (migration 1781000003 + base migration + setup
  script mirror):
    update: (@request.auth.id = id && @request.body.role:isset = false)
            || @request.auth.role = "admin"
    delete: @request.auth.role = "admin"
  Self-service onboarding keeps working (it never touches role); the
  role field is admin-only; deletion is admin-only.
- pb_hooks/team_members.pb.js: the ENTRA_ADMIN_EMAILS resync is now
  escalate-only — it guarantees admin for allow-list members on every
  login but no longer demotes, otherwise every TeamManager promotion
  would revert on the member's next sign-in (ADR-004 amended).
- TeamManager.jsx: info text updated to the new behaviour.

Verified with a two-identity mock-OIDC matrix (11/11): allow-list vs
regular login, self-escalation blocked while onboarding self-update
still works, cross-user update/delete blocked, admin promote/demote/
delete work, promotion survives the member's next login, allow-list
admin stays admin. Regression: #22 matrix 9/9, #24 matrix 8/8, #18
harness 15/15, npm test 112/112, eslint clean.

Closes #27

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

scripts/setup-pb-collections.mjs

@@ -114,6 +114,10 @@ const COLLECTIONS = [
     // Mirror of pb_migrations/1781000002: creation only via the OAuth2
     // sign-up flow (issue #22).
     createRule: '@request.context = "oauth2"',
+    // Mirror of pb_migrations/1781000003: self-update without role changes;
+    // roster management (incl. role/delete) is admin-only (issue #27).
+    updateRule: '(@request.auth.id = id && @request.body.role:isset = false) || @request.auth.role = "admin"',
+    deleteRule: '@request.auth.role = "admin"',
     passwordAuth: { enabled: false, identityFields: ['email'] },
     fields: [
       { name: 'name', type: 'text', required: false },