Render membrane drawable trees to java.awt.image.BufferedImage via
membrane's Java2D backend. Faster than SVG for large plots and
produces raster output that Clay renders automatically.

Composite plan -> membrane rendering. The CompositePlan dispatch of
the plan->membrane multimethod, plus the membrane drawables for
composite chrome (title, strip labels, shared legend).

Pure data-side composite logic -- chrome geometry, layout
computation, composite-pose->draft, composite-draft->plan -- stays
in `impl/compositor.clj`. This namespace only handles the rendering
side and depends on membrane, keeping `impl/` free of membrane
dependencies.

Build a membrane drawable tree from a plan.
Plan → membrane is format-agnostic: the drawable tree can be converted
to SVG, PNG, or any other format membrane supports.

Convert membrane drawable trees to SVG hiccup.