feat(fp): WP-23 — org-template backend + admin role

Second template axis (org identity: letterhead, footer, signature,
margins) server-side: OrgTemplateStore with JSON version history,
publish/rollback, sent-brief version pinning, admin role + capability,
5 admin endpoints, org-logo upload category. FE seam widened only
(Role/Capability unions, interceptor); WP-24/26 consume it.

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

docs/backlog/WP-22-durable-persistence.md

@@ -1,6 +1,6 @@
 # WP-22 — Durable persistence (optional tier)
 
-Status: done (pending commit)
+Status: done (556f2f4)
 Phase: 5 — productie-volwassenheid
 
 ## Why