docs: replace SHOWCASE-ROADMAP.md with docs/backlog/ (17 WPs)

Turns the prior roadmap sketch into ordered, gated work packages (enforcement
gates, FP/DDD consistency, CIBG fidelity, Storybook curriculum, a11y) from the
2026-07-02 showcase-hardening audit.

docs/backlog/WP-04-ui-not-infrastructure.md

@@ -0,0 +1,75 @@
+# WP-04 — Boundaries II: `ui ↛ infrastructure` + showcase sanction
+
+Status: todo
+Phase: 0 — enforcement & gates
+
+## Why
+
+The documented rule `ui → application → domain` (CLAUDE.md §1) is not lint-enforced, and
+three components inject infrastructure adapters directly. This is the biggest refactor of
+Phase 0 — a pure move of wiring, no behavior change.
+
+## Read first
+
+- `CLAUDE.md` §1, `docs/ARCHITECTURE.md`
+- `eslint.config.mjs`
+- `src/app/registratie/ui/registratie-wizard/registratie-wizard.component.ts` (lines
+  ~18-19: `BrpAdapter`/`parseBrpAddress`, `DuoAdapter`/`parseDuoLookup`)
+- `src/app/herregistratie/ui/intake-wizard/intake-wizard.component.ts` (~line 28:
+  `IntakePolicyAdapter`)
+- `src/app/registratie/application/big-profile.store.ts` (the facade pattern to copy)
+- `src/app/showcase/ui/concepts.page.ts`
+
+## Decisions (pre-made, don't relitigate)
+
+- **Showcase is sanctioned, not fixed**: `showcase/` is a teaching page whose point is
+  showing multiple contexts side by side. Add an explicit eslint override allowing
+  `@registratie/*` / `@herregistratie/*` from `src/app/showcase/**`, with a message
+  comment — same precedent as the existing `debug-state` exemption. Document in
+  ARCHITECTURE.md: "showcase may read every context; nothing imports showcase."
+- Move wiring only — do not redesign adapter signatures. Existing machine specs are the
+  safety net.
+
+## Files
+
+- `eslint.config.mjs` — forbid `**/ui/**` and `**/layout/**` → `**/infrastructure/**`;
+  add the showcase sanction
+- `src/app/registratie/ui/registratie-wizard/registratie-wizard.component.ts` — BRP/DUO
+  lookups move behind a registratie `application/` facade (command or store methods)
+- `src/app/herregistratie/ui/intake-wizard/intake-wizard.component.ts` — policy resource
+  moves behind **new** `src/app/herregistratie/application/` (folder doesn't exist yet)
+- `docs/ARCHITECTURE.md` — fix "three contexts, four layers" → six contexts
+  (shared, auth, registratie, herregistratie, brief, showcase), five layers (+ contracts);
+  add the showcase sanction
+- `CLAUDE.md` §1 — add `brief` to the context list; note the showcase sanction
+
+## Steps
+
+1. Create the application-layer facades (pattern: `big-profile.store.ts` /
+   `submit-*.ts` commands); components inject those instead of adapters.
+2. Add the eslint restriction; add the showcase override with rationale message.
+3. Fix any further hits lint finds (`letter-composer`'s infra import is handled in
+   WP-03; if it slipped, fix here).
+4. Update both docs' context/layer inventory.
+
+## Acceptance criteria
+
+- [ ] Rule active; lint green; no disables beyond the documented showcase + debug-state
+      exemptions.
+- [ ] No `**/ui/**` file imports from `**/infrastructure/**`.
+- [ ] Both wizards behave unchanged (specs pass; manual smoke).
+- [ ] CLAUDE.md and ARCHITECTURE.md list 6 contexts / 5 layers.
+
+## Verification
+
+GREEN + `npm run test-storybook:ci`. Manual smoke: `npm start` → run the registratie
+wizard (BRP prefill + DUO lookup steps) and the intake wizard end-to-end.
+
+## Out of scope
+
+Redesigning the adapters or resource loading; parse boundaries (WP-05).
+
+## Risks
+
+Resource wiring moving layers can subtly change injection timing — keep facades
+`providedIn: 'root'` like existing stores and hand the resource through unchanged.