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/shared/layout/wizard-shell/wizard-shell.component.ts

@@ -35,6 +35,8 @@ export type WizardStatus = 'editing' | 'submitting' | 'submitted' | 'failed';
   styles: [`
     .es-title{margin:0 0 var(--rhc-space-max-sm)}
     .es-list{margin:0;padding-inline-start:var(--rhc-space-max-xl)}
+    /* Default link color doesn't meet contrast on the error-alert's light-red surface. */
+    .es-list a{color:var(--rhc-color-lintblauw-700)}
   `],
   template: `
     @switch (status()) {