time_to_first_draw — TTFD marker

A placeholder renderable intended to mark (and later measure) the time-to-first-draw of the UI.

TimeToFirstDrawRenderable::new() -> Self

The struct carries no state and renders nothing — it is pure API scaffolding for a future TTFD instrumentation pass.

// Place it in a tree where you want to measure first draw.
let marker = TimeToFirstDrawRenderable::new();

Next: types — marker traits.