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-24-letter-canvas.md

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+# WP-24 — Letter canvas (edit on the letter)
+
+Status: todo
+Phase: 6 — Brief v2 (edit-on-the-letter, org templates, server-rendered preview)
+
+## Why
+
+The drafter should compose **on the letter** — letterhead above, footer/signature
+below, content blocks edited in place — instead of in an abstract form next to a
+separate preview. PRD Brief v2 §4. This is a **presentation rebuild only**: the
+domain model, `brief.machine.ts`, and every `BriefMsg` stay byte-identical.
+
+## Read first
+
+- PRD Brief v2 §2b (fidelity note), §4, §10; the sample `voorbeeldbrief-inschrijving.pdf`
+- `src/app/brief/ui/letter-composer/letter-composer.component.ts` (the `canEdit` pivot)
+- `src/app/brief/ui/letter-preview/letter-preview.component.ts` (rendering that migrates in)
+- `docs/backlog/WP-23-org-template-backend.md` (the `orgTemplate` on `BriefViewDto`)
+
+## Decisions (pre-made, don't relitigate)
+
+- **One stylesheet is the FE⇄BE rendering contract**: `public/letter.css` — class
+  vocabulary `.letter`, `.letter__letterhead`, `.letter__body`, `.letter__signature`,
+  `.letter__footer`, `.letter__page-break`; margins as `--letter-margin-*` custom
+  props; `@page`/print rules. Loaded via `<link>` in `index.html` (app + Storybook).
+  WP-25's backend renderer inlines the same file; its parity test is the fence.
+- **`LetterCanvasComponent`** (new organism, `Domein/Brief/Letter Canvas`) with
+  `editableRegions: 'content' | 'template' | 'none'` — one component serves drafter
+  composing, approver review (and in WP-26, the admin editor). Letter typography on
+  the canvas is the letter's, not the portal UI's — but still token-bridged.
+- `'content'` mode hosts the **existing** `letter-section`/`letter-block` components
+  unchanged; letterhead/footer/signature render read-only with a subtle tint and a
+  first-use caption ("komt uit de huisstijl van de organisatie").
+- `'none'` mode absorbs `letter-preview`'s rendering (paragraph grouping, placeholder
+  chips, sample-values toggle); **`ui/letter-preview/` is then deleted** — the PRD
+  explicitly supersedes it; no third rendering is maintained.
+- **Page-break indicator is approximate by design**: a dashed line per A4-content
+  interval with the caption "±pagina-einde — afdrukvoorbeeld is leidend" (PRD §2b
+  honesty requirement).
+- `brief.machine.ts` and `BriefMsg` are untouched — `git diff` must prove it.
+
+## Files
+
+- `public/letter.css` (new), `src/index.html` (link)
+- `src/app/brief/domain/org-template.ts` (new, pure) — `OrgTemplate` type
+- `src/app/brief/infrastructure/brief.adapter.ts` (+spec) — parse `orgTemplate`
+- `src/app/brief/ui/letter-canvas/*` (new: component + stories)
+- `src/app/brief/ui/letter-composer/letter-composer.component.ts` (pivot swap) + stories
+- `src/app/brief/ui/brief.page.ts` (pass orgTemplate through)
+- delete `src/app/brief/ui/letter-preview/*`
+
+## Steps
+
+1. `letter.css` from the sample PDF's geometry (A4 proportions, letterhead, address
+   window + reference block, footer rule, signature).
+2. `OrgTemplate` domain type + `parseOrgTemplate` boundary in the adapter (+spec).
+3. Canvas organism: three modes, zoom input, page-break indicator.
+4. Migrate `letter-preview` rendering into `'none'` mode; delete the component,
+   fold its stories into the canvas stories.
+5. Swap the composer's `@if (canEdit())` pivot for
+   `<app-letter-canvas [editableRegions]="canEdit() ? 'content' : 'none'">`.
+6. Stories: three modes + zoom + page-break, all axe-gated.
+
+## Acceptance criteria
+
+- [ ] Drafter edits blocks in place on the letter surface; passage picker and
+      diagnostics click-to-locate still work on the canvas.
+- [ ] Approver sees the identical surface read-only with the action bar.
+- [ ] Letterhead/footer/signature come from `orgTemplate` and are visibly non-editable.
+- [ ] `git diff` shows zero changes in `brief.machine.ts` / `brief.ts` Msg surface.
+- [ ] `letter-preview` is gone; no story regression (`test-storybook:ci` green).
+- [ ] Full GREEN + e2e smoke.
+
+## Verification
+
+GREEN one-liner; `npm run e2e` (brief flow); manual: `?role=drafter` compose on
+canvas, `?role=approver` review; `?scenario=slow|error` still degrade gracefully
+through `<app-async>`.
+
+## Out of scope
+
+Server-rendered preview + `[NOG IN TE VULLEN]` resolution (WP-25); admin `'template'`
+mode wiring beyond the input existing (WP-26 gives it a consumer); zoom controls
+polish + standaardbrief + diff badges (WP-27).
+
+## Risks
+
+The canvas duplicates the letter markup that WP-25's backend renderer will emit —
+acceptable *only* because `letter.css` is shared and WP-25 adds the class-parity
+test; until WP-25 lands, the canvas is the sole consumer, so no drift is possible.
+Deleting `letter-preview` breaks any deep import of it — repo-wide grep before delete.