Split platform-admin from org-owner, hide Trips from non-founding orgs

SAAS_PLAN.md B7. "admin" meant two different things before this: platform
operator (SAAS_PLAN.md's own framing) and, by accident of how
app/settings/layout.tsx was gated, the only role that could ever reach an
org's own billing/members/node-ownership settings. A paying customer who is
their own org's owner couldn't reach their own Settings page - the gate
checked isAdmin, which only platform admins ever have.

settings/layout.tsx now admits org_role === "owner" as well as platform
admins (isAdmin stays valid too, for support access to any org's
settings). Nav.tsx shows the Settings link on the same condition, and moves
Admin (the platform-operator screens: feature flags, users, audit,
correlation debug) out of the customer-facing link group entirely - it was
already gated server-side, this is just the nav no longer implying it's
part of the product.

Trips - an internal utility feature riding along on this stack, not a
tenant-scoped product surface (see [[trips-feature-intentional]]) - drops
out of the customer-facing viewer link group and only shows for the
founding org (new lib/tenancy.ts mirrors app/internal/tenancy.py's
FOUNDING_ORG_ID) or a platform admin, matching the mutation-route gating
routers/trips.py already got in the backend tenancy commit. Reads stay
open to any signed-in user, same as before - trips' own visibility model
(public/private per trip) predates and is unrelated to org tenancy, and
restricting it further wasn't asked for.

Also closes two DEFERRED.md items now that they have somewhere to write to:
app/settings/organization's "Save changes" button now actually calls
c2api.getOrg()/updateOrg() (routers/org.py, shipped in the backend tenancy
commit) instead of being permanently disabled. app/settings/nodes gained an
EnrollmentTokensPanel (mint/list/revoke against the same commit's
/org/enrollment-tokens routes) - without this, B2b's whole point (a
customer enrolls their own node with their own token instead of an
admin-issued key) had no way to actually be used outside a raw API call.

Left alone, and written up as new DEFERRED.md entries instead of guessed
at: node/system *write* routes (approve, create, delete) stay
platform-admin-only rather than being loosened to org owner/operator - a
real gap per SAAS_PLAN.md 2.4, but a separate authorization design that the
plan's 12-item build order doesn't enumerate. And settings/members +
settings/nodes' ownership table both still call GET /admin/users
(platform-admin-only) - a pure org owner who reaches the page via this
commit's gate will get 403s from it. Today's only real user is also a
platform admin, so this is invisible until a second, non-admin org owner
exists.

Typecheck: clean (tsc --noEmit via the WSL-native ~/drb-frontend copy).

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

drb-frontend/lib/tenancy.ts

@@ -0,0 +1,10 @@
+/**
+ * Mirrors drb-c2-core/app/internal/tenancy.py's FOUNDING_ORG_ID — the org
+ * every pre-tenancy document and every legacy enrollment path resolves
+ * into. Frontend-side, it's used only to gate the /trips feature (an
+ * internal utility riding along on this stack, not a tenant-scoped product
+ * surface — see [[trips-feature-intentional]] and SAAS_PLAN.md B7) to the
+ * founding org, matching the same restriction the backend already enforces
+ * in routers/trips.py.
+ */
+export const FOUNDING_ORG_ID = "founding";