paper2poster — paper_spec.md → HTML poster → PDF/PNG + editable PPTX

This skill is the rendering stage of a 3-skill pipeline. It assumes paper2assets has already produced the input <outdir>/. Given that outdir, it picks figures, renders an HTML poster, iteratively fills the layout to fit a fixed page (60×36in landscape or 33.1×46.8in A0 portrait), generates per-section narration audio, hands the HTML to the bundled html2pptx sub-skill (vendored at html2pptx/) for an editable .pptx, and exports PDF + PNG. The html2pptx handoff is a standard final step, not optional — one run yields poster.{html,pptx,pdf,png}, because users want the editable deck in the same pass and won't call html2pptx separately.