List the current user's API keys (key value never returned).

Cookie session only; uses createClient from @/lib/supabase/server + getUser, never inspects the Authorization header, so a pm_live_ Bearer token is NOT accepted. Lists keys for the authenticated user (eq user_id), sorted created_at DESC. The raw key is never returned — only keyPrefix. If admin client unavailable or api_keys table missing (code 42P01), returns 200 with { keys: [], count: 0, message }.