🐛 fix(frontend): apply server:false + route.fulfill to health spec

Closes the debt left by PR #40 (api/info + footer): the existing
tests/e2e/health.spec.ts happy path still hit the dev-proxy issue
that PR #40 worked around for the new app-footer spec.

Same fix applied to HealthDashboard.vue and the spec:
- HealthDashboard.vue: useFetch( ..., { server: false }) — fetch
  client-side only so Playwright route mocks apply (was failing on
  SSR through the dev proxy).
- health.spec.ts: happy path now uses page.route to mock /api/healthz
  with a 200 success body, matching the pattern in app-footer.spec.ts.
  The error scenario already used route mocking; unchanged.

The integration with the real backend remains covered by the BDD
scenario in features/health/health.feature (server-side, no proxy
in the loop).

Full Playwright suite (4 tests) now passes locally.

frontend/components/HealthDashboard.vue

@@ -5,7 +5,11 @@ import HealthDashboardView, { type HealthInfo } from './HealthDashboardView.vue'
 // Separation of concerns (SRP):
 //   - HealthDashboard (this) = data layer (useFetch lifecycle)
 //   - HealthDashboardView    = presentation layer (testable in Storybook + e2e)
-const { data, pending, error } = await useFetch<HealthInfo>('/api/healthz')
+//
+// server: false → fetch client-side only. Avoids SSR fetching through the dev
+// proxy (which can fail in some local setups), and lets Playwright route mocks
+// apply. Same fix that landed for AppFooter in PR #40.
+const { data, pending, error } = useFetch<HealthInfo>('/api/healthz', { server: false })
 </script>
 
 <template>