Five tasks for the sample-showcase cycle: (1) the enriched blueprint source —
LinComb import, the `signals` composite (trend = sma_cross, momentum = macd, blend
= LinComb(3) with weights[2] bound), the node-0 swap in sample_blueprint_with_sinks,
the re-pathed sweep_family axes + a showcase_prices warm-up stream; (2) re-path the
two in-crate tests (bootstrap-runs-drains, sweep odometer); (3) re-capture the
sample-model.json render fixture; (4) a new headless depth-2 nesting guard
(viewer_nested_depth.mjs + .rs); (5) the workspace build/test/clippy gate.
refs #62
