feat(fp): WP-26 — admin org-template editor

Edit the letter's org identity in place on the same canvas the drafter composes
on (editableRegions='template'): letterhead/signature/footer become inline
controls, content a read-only sample. Margins (bounded), logo upload (reuses the
shared upload transport + single-upload), version history + rollback, proefbrief,
and publish-with-impact-confirmation. House form-machine idiom
(org-template.machine.ts) + root store with debounced save. Capability-gated
(orgtemplate:edit) with a deny-by-default alert; route /brief/huisstijl.

Backend + generated client were already in place (WP-23). Also fixes a
pre-existing red check:tokens (WP-24 canvas hex fallbacks) and threads the
published logo through to the drafter's canvas.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/app/brief/application/brief.store.ts

@@ -13,6 +13,7 @@ import { BriefMsg, BriefState, initial, reduce } from '@brief/domain/brief.machi
 import { OrgTemplate } from '@brief/domain/org-template';
 import { BriefAdapter, BriefView } from '@brief/infrastructure/brief.adapter';
 import { LetterPreviewAdapter } from '@brief/infrastructure/letter-preview.adapter';
+import { uploadContentUrl } from '@shared/upload/upload.adapter';
 
 /** Transient action state (submit/approve/reject/send/resetDemo) — one tagged union
     instead of a busy boolean + a nullable error sitting side by side. */
@@ -56,6 +57,12 @@ export class BriefStore {
       stays untouched by design). Set from every server view that carries it. */
   readonly orgTemplate = signal<OrgTemplate | null>(null);
 
+  /** The org logo's content URL for the letterhead, or null when the template has none. */
+  readonly logoUrl = computed<string | null>(() => {
+    const id = this.orgTemplate()?.logoDocumentId;
+    return id ? uploadContentUrl(id) : null;
+  });
+
   /** The load lifecycle as `RemoteData`, for `<app-async>` — the machine keeps
       owning the letter's own domain lifecycle (draft/submitted/approved/…); this is
       purely a projection of its loading/failed tags onto the shared async seam. */