fix(ssp): route cancel/delete through runSubmit, surface the error (RB-20)

ApplicationsStore.cancel and AdminCasesStore.delete rolled an optimistic
write back on failure but showed no message — a bare catch with no
Result and no error channel (CQ-002). Both now call runSubmit and set a
lastError signal on failure, mirroring createSubmitChangeRequest in the
same folder. Each page renders the error with the existing app-alert
atom, the same pattern brief.page.ts already uses for lastError.

Added a spec file for ApplicationsStore (none existed) and extended
AdminCasesStore's spec, each asserting the rollback AND the surfaced
error. Verified both new assertions fail without the fix (an Edit
undo/redo of the store method, not git checkout).

Regenerated libs/shared/docs/behaviour-spec.mdx (gen:behaviour-spec) to
pick up the new/renamed test names. Marked RB-20 done in 99-backlog.md
and recorded the change in implementation/rb-20.md.

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

apps/ssp/src/app/registratie/application/admin-cases.store.spec.ts

@@ -1,5 +1,6 @@
 import { TestBed } from '@angular/core/testing';
 import { describe, it, expect, vi } from 'vitest';
+import { SUBMIT_FAILED } from '@shared/application/submit';
 import { ApplicationsAdapter } from '@registratie/infrastructure/applications.adapter';
 import { AdminCasesStore } from './admin-cases.store';
 
@@ -43,7 +44,10 @@ describe('AdminCasesStore', () => {
     expect(s.tag === 'Success' && s.value.map((c) => c.id)).toEqual(['b']);
   });
 
-  it('rolls back the removal when the delete fails', async () => {
+  // RB-20: a failed delete must not be silent — the row rolls back AND the store
+  // surfaces the error the page renders. Before RB-20 this only rolled back
+  // (bare `catch { this.state.set(before) }`), so `lastError()` stayed null forever.
+  it('rolls back the removal and surfaces the error when the delete fails', async () => {
     const deleteAny = vi.fn().mockRejectedValue(new Error('boom'));
     const store = setup({ listAll: () => Promise.resolve([summary('a')]), deleteAny });
     await store.load();
@@ -51,5 +55,24 @@ describe('AdminCasesStore', () => {
     await store.delete('a');
     const s = store.cases();
     expect(s.tag === 'Success' && s.value.map((c) => c.id)).toEqual(['a']); // reappears
+    expect(store.lastError()).toBe(SUBMIT_FAILED);
+  });
+
+  it('clears a stale error on the next delete attempt', async () => {
+    const deleteAny = vi
+      .fn()
+      .mockRejectedValueOnce(new Error('boom'))
+      .mockResolvedValueOnce(undefined);
+    const store = setup({
+      listAll: () => Promise.resolve([summary('a'), summary('b')]),
+      deleteAny,
+    });
+    await store.load();
+
+    await store.delete('a');
+    expect(store.lastError()).toBe(SUBMIT_FAILED);
+
+    await store.delete('b');
+    expect(store.lastError()).toBeNull();
   });
 });