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>

pb_hooks/team_members.pb.js

@@ -41,14 +41,17 @@ onRecordCreate(function (e) {
   e.next();
 }, "team_members");
 
-// On every successful auth (incl. OIDC): keep the admin role in sync with the
-// allow-list, so promoting/demoting an admin only requires an env change.
+// On every successful auth (incl. OIDC): guarantee the admin role for
+// allow-list members. ESCALATE-ONLY (#27): the allow-list grants admin, it no
+// longer demotes — otherwise every role promotion made through TeamManager
+// would be reverted on the member's next login. Demotion runs through
+// TeamManager; allow-list members cannot be demoted (the list wins on their
+// next login).
 onRecordAuthRequest(function (e) {
   const { resolveRole } = require(`${__hooks}/utils.js`);
   const email = e.record.get("email") || "";
-  const want = resolveRole(email);
-  if (e.record.get("role") !== want) {
-    e.record.set("role", want);
+  if (resolveRole(email) === "admin" && e.record.get("role") !== "admin") {
+    e.record.set("role", "admin");
     e.app.save(e.record);
   }
   e.next();