Add motion to a build

With canvas_builder_motion enabled, a build can also author the section's timeline — which elements move, in what order, and on what trigger. This is where the two submodules pair up: a blueprint can specify motion as part of its design, and on any existing section you can just describe the effect you want in plain language — "convert this section into a horizontal scrolling section," "stagger a fade-in across these cards," "fade up the heading and add a scroll progress bar" — and the build turns that into a real timeline, not a description of one. Combined with a full-page blueprint, this is how you get a cinematic, motion-driven landing page without hand-authoring a single animation.

The vocabulary is not a list the AI module keeps: it is read from the Motion submodule, so an effect you disable, or one a target cannot support, is not something the model can propose. Timelines are written through the motion module's public API, which validates every target and action and rejects a bad plan rather than persisting it.

With the submodule disabled, nothing here applies and no motion keys are produced.