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>

libs/shared/src/application/remote-data.spec.ts

@@ -1,6 +1,6 @@
 import { describe, it, expect } from 'vitest';
-import { RemoteData, map2, map } from './remote-data';
-import { loading, failure, success } from '../testing/remote-data';
+import { RemoteData, map2, map, successOf } from './remote-data';
+import { loading, failure, empty, success } from '../testing/remote-data';
 
 const loadingRd: RemoteData<string, number> = loading();
 const failureRd: RemoteData<string, number> = failure('x');
@@ -21,3 +21,15 @@ describe('RemoteData combinators', () => {
     expect(map2(ok(2), ok(3), add)).toEqual({ tag: 'Success', value: 5 });
   });
 });
+
+describe('successOf', () => {
+  it('unwraps a Success value', () => {
+    expect(successOf(ok(2))).toBe(2);
+  });
+
+  it('is undefined for every other state', () => {
+    expect(successOf(loadingRd)).toBeUndefined();
+    expect(successOf(failureRd)).toBeUndefined();
+    expect(successOf(empty())).toBeUndefined();
+  });
+});