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/herregistratie/ui/herregistratie-wizard/herregistratie-wizard.component.ts

@@ -5,6 +5,7 @@ import { TextInputComponent } from '@shared/ui/text-input/text-input.component';
 import { AlertComponent } from '@shared/ui/alert/alert.component';
 import { WizardShellComponent, WizardError, WizardStatus } from '@shared/layout/wizard-shell/wizard-shell.component';
 import { createStore } from '@shared/application/store';
+import { whenTag } from '@shared/kernel/fp';
 import { BigProfileStore } from '@registratie/application/big-profile.store';
 import { WizardState, WizardMsg, Draft, initial, reduce } from '@herregistratie/domain/herregistratie.machine';
 import { submitHerregistratie } from '@herregistratie/application/submit-herregistratie';
@@ -71,13 +72,13 @@ export class HerregistratieWizardComponent {
   readonly stepLabels = ['Werkervaring', 'Nascholing'];
   private stepTitles = ['Werkervaring (afgelopen 5 jaar)', 'Nascholing'];
 
-  private editing = computed(() => (this.state().tag === 'Editing' ? (this.state() as Extract<WizardState, { tag: 'Editing' }>) : null));
+  private editing = computed(() => whenTag(this.state(), 'Editing'));
   protected step = computed(() => this.editing()?.step ?? 1);
   protected draft = computed<Draft>(() => this.editing()?.draft ?? { uren: '', jaren: '', punten: '' });
   protected errUren = computed(() => this.editing()?.errors.uren ?? '');
   protected errJaren = computed(() => this.editing()?.errors.jaren ?? '');
   protected errPunten = computed(() => this.editing()?.errors.punten ?? '');
-  protected failedError = computed(() => (this.state().tag === 'Failed' ? (this.state() as Extract<WizardState, { tag: 'Failed' }>).error : ''));
+  protected failedError = computed(() => whenTag(this.state(), 'Failed')?.error ?? '');
 
   // --- Presentational wiring for the shared wizard shell ---------------------
   protected stepTitle = computed(() => this.stepTitles[this.step() - 1]);