rev 192

Closes the named rev-191 next-sprint candidate (per-category OG cards on the new /templates/by-category/{category} pages) at the social-share polish axis + opens a standalone industry-category taxonomy endpoint at GET /api/v1/onboarding-templates/categories so MCP hosts rendering 'browse Loop Desk's industry coverage at the category level' don't have to enumerate the rev-172 full listing + aggregate client-side — mirrors the rev-104 /api/v1/blog/categories pattern at the templates axis on the category dimension + closes two more rev-191-named radar candidates at the templates axis (small independent print shops with named-quote-to-PO + named-press-utilisation + named-rerun warranty discipline + named-stock-and-substrate continuity, and independent music schools with named-private-lesson cadence + named-recital programming + named-instructor continuity + named-tuition-cycle discipline) bringing the templates cluster to fifty-seven named verticals + extending the rev-78 OpenAPI typed-coverage cadence to its 100th unbroken rev. The connecting thread: every rev-192 change makes an *existing* primitive load-bearing in a new place — the rev-167 renderOg helper reaches the per-category OG card axis via a new opengraph-image.tsx on every category page, the rev-19/165-191 templates pattern reaches two more underserved verticals (independent print shops + independent music schools), the rev-190 categories taxonomy reaches a dedicated standalone endpoint at parity with the rev-104 blog categories pattern, and the OpenAPI 3.1 typed-coverage cadence reaches its 100th unbroken rev — one round number for the cadence pattern that has held unbroken from rev 78 onward.