Why: the admin zone could not host plugin-declared partitions - KTD4
requires the RDM audit partition to be reachable by RDM domain admins and
base superadmins without hardcoding RDM into the base AdminZone.
Evidence: go test ./internal/app ./internal/server ./pkg/extension green
incl. new admin-zone recording/endpoint tests; surface snapshot test
green after surface.txt update; CI (Dev composite) is authoritative.
Impact: extension surface 2.8.0 -> 2.9.0 (Registry.AddAdminZone +
AdminZoneSpec, fail-closed on invalid specs); applyCompiled records
declarations into the plugin summary; new authenticated GET
/api/admin-zone/sections returns the flattened, ordered declaration list.
Entry visibility stays metadata-only - data capability remains enforced
by each section's own command surface (fail-closed).
Refs: WP3-I3/KTD4; task card feature-adminzone-plugin-sections.