feat(plugins): catalog images and purchase receipt uploads

Catalog items can store up to three photos; remote tenants attach a receipt on pending requests.

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

prisma/migrations/20260908120000_plugin_store_images_receipt/migration.sql

@@ -0,0 +1,2 @@
+ALTER TABLE "plugin_catalog_items" ADD COLUMN IF NOT EXISTS "images" JSONB;
+ALTER TABLE "plugin_purchase_requests" ADD COLUMN IF NOT EXISTS "receipt_url" TEXT;