fix(visualization): substitute D3 script tags before graph data

The D3 placeholder replacement ran over the already-interpolated graph
JSON, so repo-derived content literally named __D3_SCRIPTS__ was expanded
into script markup inside the graphData script, truncating it and
promoting the remaining JSON to live HTML. Substitute the trusted
template placeholders scripts-first, data-last, and add a regression
test with a node named __D3_SCRIPTS__ and an HTML-shaped symbol name.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FmPUotoqsNWWt3b41FMjwv