feat(brief): letter composition + two-person approval (teaching slice)

New `brief` context — a letter-composition feature with a drafter/approver
approval workflow, built as a teaching vertical slice on the repo's existing
FP + Elm + atomic-design patterns (see plan in ~/.claude/plans).

Domain (pure):
- Rich text as a serialisable value tree (placeholders are first-class nodes),
  moved to @shared/kernel/rich-text.ts so the shared editor can use it.
- lintPlaceholders: a pure, total content -> Diagnostic[] linter, derived never stored.
- brief.machine.ts: status sum-type with guarded transitions; frozen-snapshot =
  deep value copy; derived diagnostics/editability. Full specs.

Backend (.NET stub):
- BriefStore + seed, GET/PUT /brief and submit/approve/reject/send endpoints,
  role via X-Role header (mirrors X-Admin), transition + approver!=drafter guards,
  audit logging. Regenerated typed client via gen:api. +6 backend tests.

Seam:
- brief.adapter.ts maps flat wire unions <-> domain discriminated unions at the
  parse boundary (+ spec).

UI (atomic):
- shared atoms: checkbox, placeholder-chip; molecule: rich-text-editor (no-dep
  contenteditable, DOM<->RichTextBlock round-trip tested).
- brief/ui: letter-block, passage-picker, diagnostics-panel, rejection-comments,
  letter-section, letter-composer, letter-preview, brief.page + /brief route.
- Dev-only ?role=drafter|approver toggle + roleInterceptor; dashboard nav link.

Enforcement: @brief/* alias + eslint layer boundary (brief depends only on shared).

Also included (same session):
- Value-object specs (postcode/uren/big-nummer) — closes the "domain must have a spec" gap.
- src/docs/ Storybook MDX foundation pages (atomic design, tokens, FP-in-UI).
- .storybook/tsconfig.json: add @angular/localize to types (Storybook was fully
  broken — $localize unresolved — dev + build).

Verified: 168 FE tests, 68 backend tests, lint/build/check:tokens green,
Storybook boots, end-to-end HTTP smoke (self-approve 403, approver 200, full flow).

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

src/app/app.routes.ts

@@ -14,6 +14,7 @@ export const routes: Routes = [
       { path: 'registreren', canActivate: [authGuard], loadComponent: () => import('@registratie/ui/registratie.page').then(m => m.RegistratiePage) },
       { path: 'herregistratie', canActivate: [authGuard], loadComponent: () => import('@herregistratie/ui/herregistratie.page').then(m => m.HerregistratiePage) },
       { path: 'intake', canActivate: [authGuard], loadComponent: () => import('@herregistratie/ui/intake.page').then(m => m.IntakePage) },
+      { path: 'brief', canActivate: [authGuard], loadComponent: () => import('@brief/ui/brief.page').then(m => m.BriefPage) },
       { path: 'concepts', loadComponent: () => import('./showcase/concepts.page').then(m => m.ConceptsPage) },
       { path: '**', redirectTo: 'login' },
     ],