refactor: split dashboard.page.ts into per-concern sections

Each dashboard section (Mijn aanvragen, Wat moet ik regelen, Mijn
registratie, Specialismen, Wat wilt u doen, Beheer) now owns its own
store access, async state, and template. DashboardPage becomes pure
composition.

Extract the repeated RemoteData Success-narrowing pattern into
successOf() and the dashboard sort/split logic into
sortForDashboard/concepten/ingediend, both with tests.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

apps/ssp/src/app/registratie/ui/dashboard/specialismen.section.stories.ts

@@ -0,0 +1,51 @@
+import type { Meta, StoryObj } from '@storybook/angular';
+import { applicationConfig } from '@storybook/angular';
+import { SpecialismenSection } from './specialismen.section';
+import { BigProfileStore } from '@registratie/application/big-profile.store';
+import { Aantekening } from '@registratie/domain/registration';
+import { RemoteData } from '@shared/application/remote-data';
+import { loading, success, empty, failure } from '@shared/testing/remote-data';
+
+const rows: Aantekening[] = [
+  { type: 'Specialisme', omschrijving: 'Huisartsgeneeskunde', datum: '2016-04-12' },
+  { type: 'Aantekening', omschrijving: 'Erkend opleider huisartsgeneeskunde', datum: '2019-01-08' },
+];
+
+/** Minimal store stand-in — only the members the section's template reads. */
+function storeStub(aantekeningen: RemoteData<Error | undefined, Aantekening[]>) {
+  return { aantekeningen: () => aantekeningen, reloadAantekeningen: () => {} };
+}
+
+const meta: Meta<SpecialismenSection> = {
+  title: 'Domein/Registratie/Dashboard/Specialismen',
+  component: SpecialismenSection,
+};
+export default meta;
+type Story = StoryObj<SpecialismenSection>;
+
+export const Loading: Story = {
+  decorators: [
+    applicationConfig({
+      providers: [{ provide: BigProfileStore, useValue: storeStub(loading()) }],
+    }),
+  ],
+};
+export const Loaded: Story = {
+  decorators: [
+    applicationConfig({
+      providers: [{ provide: BigProfileStore, useValue: storeStub(success(rows)) }],
+    }),
+  ],
+};
+export const Empty: Story = {
+  decorators: [
+    applicationConfig({ providers: [{ provide: BigProfileStore, useValue: storeStub(empty()) }] }),
+  ],
+};
+export const Failed: Story = {
+  decorators: [
+    applicationConfig({
+      providers: [{ provide: BigProfileStore, useValue: storeStub(failure(new Error('offline'))) }],
+    }),
+  ],
+};