✨ feat(frontend): Storybook + auto-generated Playwright e2e docs with screenshots

Adds three things to make frontend PRs reviewable directly from Gitea web UI:

1. Storybook 8 for Vue 3 components
   - .storybook/main.ts + preview.ts
   - HealthDashboard.stories.ts (1 example story)
   - npm run storybook / npm run build-storybook

2. Playwright JSON reporter + screenshot on every test
   - playwright.config.ts: json reporter + screenshot: 'on'
   - health.spec.ts: explicit screenshot path

3. Auto-generated markdown docs with breadcrumbs
   - scripts/generate-test-docs.mjs: reads results.json -> generates docs/e2e/<test>.md per test
   - docs/README.md: top-level frontend docs index
   - docs/e2e/README.md: e2e index with link to each test
   - Each test markdown has breadcrumb [<- Back to index]
   - Screenshots embedded via relative path

Companion to PR #25 (Nuxt scaffold).

Out of scope (future PRs):
- Visual regression testing
- Storybook deployment / hosted preview
- More e2e test coverage

🤖 Co-Authored-By: Mistral Vibe <vibe@mistral.ai>

frontend/docs/README.md

@@ -0,0 +1,4 @@
+# Frontend Docs
+
+- [E2E Test Reports](./e2e/README.md) - auto-generated by `npm run docs:gen`
+- Storybook (run locally: `npm run storybook` ; build: `npm run build-storybook` then open `storybook-static/index.html`)