List templates

Lists public email templates under { data, pagination }. Each row is FULL — it carries the rendered html + previewImage plus the display metadata (title, category, brand, updatedAt), so you never need a follow-up get-one round-trip. Supports exact ?brand= and ?category= filters and a lightweight ?semantic= text filter. Templates are organization-wide references (use one as referenceEmailId on POST /v1/emails).