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-09-pure-logic.md

@@ -0,0 +1,72 @@
+# WP-09 — Pure-logic closure: dates + missing command specs
+
+Status: todo
+Phase: 1 — FP/DDD core
+
+## Why
+
+Three hand-rolled copies of the same `nl-NL {day: numeric, month: long, year: numeric}`
+formatter exist with divergent signatures, while other components use the Angular `date`
+pipe — two mechanisms plus drift risk. And two application commands with real logic have
+no spec despite "domain and pure logic must have a spec" (CLAUDE.md §5).
+
+## Read first
+
+- `src/app/registratie/domain/tasks.ts` (~line 15, `formatNL(d: Date)`)
+- `src/app/registratie/ui/aanvraag-block/aanvraag-block.component.ts` (~line 96,
+  `formatNL(iso?: string)`)
+- `src/app/brief/ui/letter-preview/letter-preview.component.ts` (~line 96, inline copy)
+- `src/app/registratie/application/draft-sync.ts` (debounce logic)
+- `src/app/registratie/application/submit-change-request.ts`
+- `src/app/app.config.ts` (LOCALE_ID `nl` is already set)
+
+## Decisions (pre-made, don't relitigate)
+
+- **Templates use `DatePipe`; pure TS uses one `formatDatumNl`** in
+  `src/app/shared/kernel/datum.ts` (Intl.DateTimeFormat, accepts ISO string | Date,
+  empty-safe). Rule goes into CLAUDE.md conventions.
+- Kernel naming is Dutch (`datum.ts`) — it formats for the Dutch UI; if that clashes with
+  the "shared = English" rule during implementation, `format-date-nl.ts` is the
+  alternative — pick one and note it here.
+
+## Files
+
+- New `src/app/shared/kernel/datum.ts` + `datum.spec.ts`
+- The three formatter copies (delete, redirect to pipe or kernel fn)
+- New `src/app/registratie/application/draft-sync.spec.ts`
+- New `src/app/registratie/application/submit-change-request.spec.ts`
+- `CLAUDE.md` conventions (one line: DatePipe in templates, `formatDatumNl` in pure TS)
+
+## Steps
+
+1. Write `formatDatumNl` + spec (pin exact expected strings, e.g. `2 juli 2026`;
+   undefined/empty → `''`).
+2. Replace the three copies; templates that can use the pipe use the pipe.
+3. `draft-sync.spec.ts` with vitest fake timers: coalescing (n rapid changes → 1 sync),
+   trailing call, flush-on-submit if applicable.
+4. `submit-change-request.spec.ts`: ok path, error path (stubbed client), Result shape.
+5. Also sweep the tiny dead exports flagged in the audit: remove unused `map3` from
+   `shared/kernel/fp.ts` (verify unused first) and the never-set `variant` input on
+   `confirmation.component.ts`.
+
+## Acceptance criteria
+
+- [ ] Exactly one hand-written date formatter in the repo; `grep -rn "toLocaleDateString" src/app`
+      hits only `datum.ts`.
+- [ ] Both command specs exist; debounce coalescing + error path covered.
+- [ ] `map3` / unused `variant` input removed (or a note here why kept).
+- [ ] CLAUDE.md rule added.
+
+## Verification
+
+GREEN + `npm run test-storybook:ci`.
+
+## Out of scope
+
+`Result` combinators (map/andThen/fold) — nice-to-have from the old roadmap, not in this
+backlog.
+
+## Risks
+
+Node ICU vs browser locale output differences — the spec pins strings; if CI's Node lacks
+full ICU (it shouldn't on Node 24), pin via `Intl.DateTimeFormat('nl-NL', …)` explicitly.