Backend: add blockers[] and warnings[] to GET /api/templates/status. Calls
validate_template() on downloaded templates; returns empty lists if not
downloaded. 3 new tests (10 total, all passing).
Frontend (templates.js): filterable/sortable table with readiness badges
(Blocked/Caveats/Ready/Migrated/Needs Update), bulk-select toolbar,
per-row migrate/detail buttons, and template detail view with 3 tabs
(Overview, Issues, Migration History).
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>