Persist tutorial quarantine results in DB + Admin UI view (currently discarded on CI runner) #2585

Problem

Tutorials that fail pre-publish validation are quarantined by scripts/validate-tutorials.ts, which renameSyncs the offending .md into .tutorial-cache/quarantine/ and writes errors.json, then exits 0. This directory lives only on the ephemeral GitHub Actions runner for rebuild-content.yml and is discarded when the run ends. Nothing consumes errors.json; there is no alert and no Admin UI surface. The quarantine is effectively write-only garbage.

Consequence: a tutorial can silently drop out of the ACTIVE content snapshot (and 404 on PROD) with no durable record of why. Confirmed live for btp-transport-management-cpi-01-use-case (0 steps after sap-tutorials/Tutorials#24233) and private-link-gcp (0 steps), among others.

Ask

Store quarantine results centrally in the DB and expose them in the Admin UI so they aren't lost.

Acceptance criteria

• New persistence (e.g. QuarantineEvents entity) capturing, per quarantined slug per build: slug, reason, sourceRepo, contentVersion/manifestVersion, runId/workflowUrl, createdAt.
• validate-tutorials.ts (or the workflow step) writes these rows to HANA via an authenticated endpoint instead of (or in addition to) the throwaway errors.json.
• Admin UI view listing current quarantined tutorials with reason, source repo, and last-seen build; sortable/filterable; links to the source file.
• A quarantined slug that later validates cleanly is cleared/aged-out so the view reflects current state, not history-forever.
• Reporting: count of quarantined tutorials over time / per repo.

Context / pointers

• scripts/validate-tutorials.ts — the gate (never exits non-zero; writes errors.json at .tutorial-cache/quarantine/).
• .github/workflows/rebuild-content.yml — runs npm run validate-tutorials.
• Carry-forward of unchanged slugs between content versions masks these failures until a full rebuild drops the quarantined slug (see also the "pre-publish validators silently broken, hidden by carry-forward" known failure mode).

Related: #2 (Admin Rebuild loses these errors silently), #3 (PROD serve-time 404s).