Create a new funnel in the workspace.

Creating a funnel automatically creates a workflow. You can then add pages to the funnel by creating pages with funnel.funnel_id set to the new funnel's ID (see the Create Page endpoint).

Client flow for building a funnel with pages:

1. POST /api/v2/workspaces/:id/funnels — creates the funnel (workflow auto-created)
2. POST /api/v2/workspaces/:id/pages with { page: { name: "...", funnel: { funnel_id: "<funnel_id>" }, markup: "<PML string>" } } — creates each page, auto-links it to the funnel, and applies the markup in one call
3. PATCH /api/v2/pages/:id with { page: { markup: "<PML string>" } } — applies or updates visual content (PML markup) on an existing page
4. Steps 2 and 3 can be combined: passing markup in the create call sets the initial visual content without a separate PATCH

The internal step/workflow wiring is handled automatically — API clients never need to manage workflows or steps directly.