Bundled named templates, expanded by Plotly.Figure.to_render_json/1.

The definitions come from Plotly.py and work without a browser template registry. Names may be strings or atoms. Combine templates with + ("plotly_dark+presentation"): they deep-merge left to right, later ones winning. Inline template maps pass through unchanged. An unknown name (or unknown part of a combined name) logs a warning and is skipped, so the chart renders without it; faithful figure JSON retains the original name.