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).

CLAUDE.md

@@ -68,7 +68,7 @@ Default reflex — **if you're about to add a second/third boolean to track stat
 model a discriminated union instead.** Three tools, all in `shared/application`:
 
 - **`RemoteData<E,T>`** (`remote-data.ts`) — `Loading | Empty | Failure{error} | Success{value}`.
-  Combine sources with `map`/`map2`/`map3`/`andThen` (Failure > Loading > Success).
+  Combine sources with `map`/`map2`/`andThen` (Failure > Loading > Success).
   Render it via the `<app-async>` molecule (`shared/ui/async`) — one of four
   templates, mutually exclusive by construction. Default loading spinner/skeleton
   is delay-gated (~250ms) so fast connections don't flash.
@@ -145,6 +145,11 @@ not heavy component tests.
   (Model/Msg/reduce) + value objects + a `submit-*` command returning `Result` — the
   same shape as the wizards, whether it's one step or many. Don't hand-roll mutable
   fields + ad-hoc error signals.
+- **Dates: `DatePipe` in templates, `formatDatumNl` in pure TS.** A template formats a
+  date with Angular's `DatePipe` (`| date: 'longDate'`); pure TS that can't reach a pipe
+  (a domain function, a `$localize` string) uses the one hand-written
+  `formatDatumNl` (`shared/kernel/datum.ts`). Never a third hand-rolled
+  `toLocaleDateString` call.
 - Routes: lazy `loadComponent`, persistent `ShellComponent` parent, `canActivate:
 [authGuard]` on protected routes (`app.routes.ts`).
 - Theming: CIBG Huisstijl (a customized Bootstrap 5.2 build) is vendored under