Custom Viz - HTML Renderer

Dashboard Studio's markdown panel is deliberately limited — no styled spans, no inline SVG, no data-driven HTML. **HTML Renderer** fills that gap with a custom visualization that renders a HTML template you control, optionally populated from your search results. Use it for branded dashboard headers, "● LIVE" status badges, colour-coded callouts, custom legends, KPI ribbons, inline SVG diagrams/floor-plans, and any rich layout the native panels can't express. Values from the primary data source can be injected with simple `{{field}}` placeholders, so the HTML can reflect live search results (e.g. `Last update: {{latest_time}}`). The renderer is **theme-aware** — it exposes Splunk's CSS variables so your markup automatically matches light/dark dashboards. Script execution is **disabled by default** and only enabled via an explicit, clearly-labelled "Allow Scripts (DANGEROUS)" option, so the default behaviour is safe static HTML. Standard `studio_visualization` custom viz, dependency-free.