Playground demo: harness projection panels (worktracks / rules / memory / residual) laid out as one dashboard.

Exercises the real Raxol.UI.Components.Harness.* panel modules -- each init/1 + render/2 directly, the same way DemoHelpers.rich_text/2 mounts Display.Text -- with sample data shaped like the materialized views these panels fold from extract{class, op, item} / residual meta events (see docs/proposals/in-flight/harness-spec-frontend.md §3).