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/registratie-wizard/registratie-wizard.component.ts

@@ -11,6 +11,7 @@ import { WizardShellComponent, WizardError, WizardStatus } from '@shared/layout/
 import { ASYNC } from '@shared/ui/async/async.component';
 import { AddressFieldsComponent } from '@registratie/ui/address-fields/address-fields.component';
 import { createStore } from '@shared/application/store';
+import { whenTag } from '@shared/kernel/fp';
 import { RemoteData, fromResource } from '@shared/application/remote-data';
 import { BrpAdapter, parseBrpAddress } from '@registratie/infrastructure/brp.adapter';
 import { DuoAdapter, parseDuoLookup } from '@registratie/infrastructure/duo.adapter';
@@ -180,13 +181,13 @@ export class RegistratieWizardComponent {
   readonly state = this.store.model;
   readonly dispatch = this.store.dispatch;
 
-  private invullen = computed(() => (this.state().tag === 'Invullen' ? (this.state() as Extract<RegistratieState, { tag: 'Invullen' }>) : null));
+  private invullen = computed(() => whenTag(this.state(), 'Invullen'));
   protected cursor = computed(() => this.invullen()?.cursor ?? 0);
   protected draft = computed<Draft>(() => this.invullen()?.draft ?? { antwoorden: {} });
   protected step = computed<StepId>(() => STEPS[Math.min(this.cursor(), STEPS.length - 1)]);
   protected stepTitle = computed(() => this.stepTitles[Math.min(this.cursor(), this.stepTitles.length - 1)]);
-  protected referentie = computed(() => (this.state().tag === 'Ingediend' ? (this.state() as Extract<RegistratieState, { tag: 'Ingediend' }>).referentie : ''));
-  protected failedError = computed(() => (this.state().tag === 'Mislukt' ? (this.state() as Extract<RegistratieState, { tag: 'Mislukt' }>).error : ''));
+  protected referentie = computed(() => whenTag(this.state(), 'Ingediend')?.referentie ?? '');
+  protected failedError = computed(() => whenTag(this.state(), 'Mislukt')?.error ?? '');
 
   // --- Presentational wiring for the shared wizard shell ---------------------
   protected primaryLabel = computed(() => (this.step() === 'controle' ? 'Registratie indienen' : 'Volgende'));