Add workshops CMS API with schedule, registrations, and public storefront routes.

Includes SQL migrations, Prisma models, dashboard CRUD, registration status workflow, and website OpenAPI updates for workshop listing and signup.

Co-authored-by: Cursor <cursoragent@cursor.com>

database/migrations/066_workshop_duration_text.sql

@@ -0,0 +1,11 @@
+-- Replace fixed minute duration with free-text duration label
+
+ALTER TABLE workshops
+  ADD COLUMN duration VARCHAR(100);
+
+UPDATE workshops
+SET duration = duration_minutes::text || ' minutes'
+WHERE duration_minutes IS NOT NULL;
+
+ALTER TABLE workshops
+  DROP COLUMN duration_minutes;