Adds a new topic to the global catalog. The topics.name column is case-insensitive (citext) and unique — if a topic with the given name already exists (any case), the existing row is returned with HTTP 200 and meta.created = false so the client can show a "Topic already exists — selected" toast (MED-832 AC7).

Newly created topics return HTTP 201 with meta.created = true. The new topic is is_active = true and gets display_order = MAX + 1.

{
  "name": "Group Formation"
}

{
  "data": {
    "name": "Active Listening"
  }
}