test: split multi-assertion specs into single-behavior tests

One behavior per test across FE machine/store specs and backend endpoint
tests, so a failure names exactly what broke.

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

src/app/herregistratie/domain/intake.machine.spec.ts

@@ -136,9 +136,13 @@ describe('submit', () => {
     expect((withScholing as any).data.punten).toBe(200);
   });
 
-  it('resolve maps Submitting to Submitted / Failed', () => {
+  it('resolve maps Submitting to Submitted on a successful submit', () => {
     const submitting = submit(answering(complete));
     expect(resolve(submitting, ok(undefined)).tag).toBe('Submitted');
+  });
+
+  it('resolve maps Submitting to Failed on a failed submit', () => {
+    const submitting = submit(answering(complete));
     expect(resolve(submitting, err('boom')).tag).toBe('Failed');
   });
 });