Step 2 (code quality): dedup + stop FE recomputing a server rule

- H1: tasksFromProfile takes the server's eligibleForHerregistratie decision
  instead of recomputing isHerregistratieEligible — the FE renders the rule,
  doesn't own it (ADR-0001). Policy reference impl kept for tests.
- M1: one shared runSubmit(fn, fallback) wrapper; the 4 submit-* commands keep
  only their payload mapping. +spec.
- M2: whenTag() kernel helper removes 10 repeated `as Extract<U,{tag}>` casts
  across the wizard/form components.

M4 (shared JA_NEE) folded into the upcoming i18n pass (clean dedup needs
$localize labels to sit in shared without breaking the English-shared-UI rule).
L1 already resolved by the restyle commit.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/app/registratie/ui/change-request-form/change-request-form.component.ts

@@ -4,6 +4,7 @@ import { HeadingComponent } from '@shared/ui/heading/heading.component';
 import { AlertComponent } from '@shared/ui/alert/alert.component';
 import { AddressFieldsComponent, AdresValue, AdresErrors } from '@registratie/ui/address-fields/address-fields.component';
 import { createStore } from '@shared/application/store';
+import { whenTag } from '@shared/kernel/fp';
 import { State, Msg, initial, reduce } from '@registratie/domain/change-request.machine';
 import { submitChangeRequest } from '@registratie/application/submit-change-request';
 import { ApiClient } from '@shared/infrastructure/api-client';
@@ -55,10 +56,10 @@ export class ChangeRequestFormComponent {
   readonly state = this.store.model;
   protected dispatch = this.store.dispatch;
 
-  private editing = computed(() => (this.state().tag === 'Editing' ? (this.state() as Extract<State, { tag: 'Editing' }>) : null));
+  private editing = computed(() => whenTag(this.state(), 'Editing'));
   protected errors = computed<AdresErrors>(() => this.editing()?.errors ?? {});
-  protected failedError = computed(() => (this.state().tag === 'Failed' ? (this.state() as Extract<State, { tag: 'Failed' }>).error : ''));
-  protected referentie = computed(() => (this.state().tag === 'Submitted' ? (this.state() as Extract<State, { tag: 'Submitted' }>).referentie : ''));
+  protected failedError = computed(() => whenTag(this.state(), 'Failed')?.error ?? '');
+  protected referentie = computed(() => whenTag(this.state(), 'Submitted')?.referentie ?? '');
 
   /** The address shown in the fields — the live draft while editing, the parsed
       data while submitting/failed (so the user sees what they sent). */