feat(a11y): WP-01 — axe-on-every-story CI gate

Turn the interactive Storybook a11y addon into a build gate:
- @storybook/test-runner + axe-playwright over the static build
  (.storybook/test-runner.ts reads the a11y tags from story context)
- test-storybook / test-storybook:ci scripts; storybook-a11y CI job
- triage: escape-hatch a11y.disable on stories whose display:contents
  wrapper splits <ul>/<li> or <dl>/<dt>/<dd> (structural, deferred to
  WP-11/WP-12, each with justification + cross-ref)
- fix trivial violations: footer/wizard-shell contrast, text-input label,
  wizard stories missing provideApiClient

Verified: broken story fails the gate; 133 stories pass.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/app/registratie/ui/registration-summary/registration-summary.stories.ts

@@ -13,6 +13,11 @@ const base = {
 const meta: Meta<RegistrationSummaryComponent> = {
   title: 'Organisms/Registration Summary',
   component: RegistrationSummaryComponent,
+  parameters: {
+    // Structural: app-data-row's host sits between the <dl> and its <dt>/<dd> —
+    // fixed by the WP-12 Datablock rework. See docs/backlog/WP-12-datablock.md.
+    a11y: { disable: true },
+  },
 };
 export default meta;
 type Story = StoryObj<RegistrationSummaryComponent>;