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/README.md

@@ -48,7 +48,7 @@ for its existing violations, so every WP ends green.
 | [WP-06](WP-06-typed-async.md)           | Generic async template contexts — kill `$any()`              | 1 · FP/DDD                  | done   |
 | [WP-07](WP-07-brief-idioms.md)          | Brief on the shared idioms + RemoteData MDX                  | 1 · FP/DDD                  | done   |
 | [WP-08](WP-08-store-idiom.md)           | One store idiom + machine naming + TEA MDX                   | 1 · FP/DDD                  | done   |
-| [WP-09](WP-09-pure-logic.md)            | Pure-logic closure: dates + missing command specs            | 1 · FP/DDD                  | todo   |
+| [WP-09](WP-09-pure-logic.md)            | Pure-logic closure: dates + missing command specs            | 1 · FP/DDD                  | done   |
 | [WP-10](WP-10-button-fidelity.md)       | CIBG button fidelity                                         | 2 · CIBG                    | todo   |
 | [WP-11](WP-11-markup-fidelity.md)       | CIBG markup fidelity: application-link + absent-class triage | 2 · CIBG                    | done   |
 | [WP-12](WP-12-datablock.md)             | CIBG Datablock for application data                          | 2 · CIBG                    | done   |