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/ARCHITECTURE.md

@@ -214,7 +214,7 @@ profile = computed(() =>
 The rule baked into `map2`: the combined result is a **Failure if either
 failed**, **Loading if either is still loading**, and only **Success when both
 succeeded**. So the page renders one state and the combiner callback only runs
-when it's safe. (`map`, `map3`, `andThen` are variations on the same idea.)
+when it's safe. (`map`, `andThen` are variations on the same idea.)
 
 ### 2c. The store — "all state changes go through one pure function"