Download rendered artifacts
Renders GIF/MP4/SVG/WEBM on demand via https://atmos-pro.com/casts/cloudposse/atmos/main/website/static/casts/screengrabs/atmos-mcp-start--help.cast.{format}. Handles the render service's three response shapes: an already-rendered artifact (downloads immediately), a still-rendering one (polls on Retry-After, capped at ~60s), and a hard error — shown inline beneath the selected format button above, whether it's a JSON error body, a generic HTTP status, or a network failure.
