feat(fp): WP-09 — pure-logic closure: dates + missing command specs

Consolidate four hand-rolled nl-NL date formatters (tasks.ts, aanvraag-
block, letter-preview, aanvraag-view -- one more than the WP found) into
one shared/kernel/datum.ts::formatDatumNl, spec-pinned and empty-safe.
Add the two missing command specs CLAUDE.md's testing rule calls for:
draft-sync.spec.ts (debounce coalescing + trailing-call + submit Result
shape, via fake timers) and submit-change-request.spec.ts. Remove the
unused RemoteData.map3 (updating the three docs that mentioned it); the
variant input on confirmation.component.ts was already gone. Documents
both stale-WP-text corrections in the backlog file.

This closes out backlog Phase 1 (FP/DDD core, WP-05..09).

docs/backlog/WP-09-pure-logic.md

@@ -1,6 +1,6 @@
 # WP-09 — Pure-logic closure: dates + missing command specs
 
-Status: todo
+Status: done
 Phase: 1 — FP/DDD core
 
 ## Why
@@ -51,15 +51,28 @@ no spec despite "domain and pure logic must have a spec" (CLAUDE.md §5).
 
 ## 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.
+- [x] Exactly one hand-written date formatter in the repo. `formatDatumNl` uses
+      `Intl.DateTimeFormat(...).format()` rather than `.toLocaleDateString()`, so
+      `grep -rn "toLocaleDateString" src/app` now hits **nothing** (stronger than the
+      literal criterion, same intent — no file anywhere hand-rolls date formatting).
+- [x] Both command specs exist; debounce coalescing + error path covered
+      (`draft-sync.spec.ts`, `submit-change-request.spec.ts`).
+- [x] `map3` removed (found in `shared/application/remote-data.ts`, not
+      `shared/kernel/fp.ts` as the WP text guessed — updated the three docs that
+      mentioned it: CLAUDE.md, `docs/ARCHITECTURE.md`, `remote-data.mdx`). The
+      `variant` input on `confirmation.component.ts` no longer exists — already
+      cleaned up before this WP ran; nothing to do.
+- [x] CLAUDE.md rule added (`Conventions` — DatePipe in templates, `formatDatumNl` in
+      pure TS).
 
 ## Verification
 
-GREEN + `npm run test-storybook:ci`.
+GREEN + `npm run test-storybook:ci` (208 unit tests, up from WP-08's 201 by the 7 new
+specs; 137 Storybook/a11y unchanged). Manual smoke via a running `docker compose` stack +
+Playwright: dashboard's herregistratie-deadline task text ("Verleng uw registratie vóór 1
+maart 2027"), the Concept aanvraag-block's complete-before text ("Rond de aanvraag af
+vóór 2 augustus 2026"), and `formatDatumNl` unit specs for the letter-preview's `today` —
+all render the expected long-form Dutch date, no console errors.
 
 ## Out of scope