List Archetypes

List system archetypes visible to any logged-in user.

Excludes archetypes flagged is_system_internal (those are for special internal flows that template authors shouldn't pick from). Returns the fields the template editor + dashboard need; intentionally omits prompt_section from the list response (callers don't need the full body when picking; admins use the dedicated admin endpoint to read it). opening_style / bridge_directive are included so the template editor can show the opening posture a template inherits from its archetype.