Merge PR #89: oEmbed provider + JSON API endpoints

[avrabe]

Context

PR #89 (feat/oembed-grafana-api-clean) is ready to merge. All CI checks pass except mutation testing (needs timeout-minutes: 20 which is in the PR).

What's in it

• /oembed endpoint (rich-type, iframe to /embed/artifacts/{id})
• /api/v1/health, /api/v1/stats, /api/v1/artifacts, /api/v1/diagnostics, /api/v1/coverage
• CORS on /api/v1/, CSP frame-ancestors *
• oEmbed discovery <link> on artifact detail pages
• 21 integration tests + 31 Playwright E2E tests
• Flaky test fixes (reload timeout, server startup timeout, fetch retry)

Action

1. Verify CI is green (mutation testing should pass with 20-min timeout)
2. Merge PR feat(api): oEmbed provider and Grafana JSON API endpoints #89
3. Delete the branch

PR: #89