v8.1.0

Phase T migration. Every diagram on the docs site (L2 topology /
dataflow / hand-authored conceptual .dot files) now renders
client-side via @hpcc-js/wasm-graphviz. The build-time
graphviz/dot system binary requirement is gone — apt-get install graphviz deleted from every CI / Release / Pages
runner.

What changed

• common/handbook/diagrams.py: every render_* helper now
  returns a graphviz DOT source string (via Digraph().source)
  instead of pre-rendered SVG. Reuses the existing
  _build_*_graph builders untouched — only the output shape
  changed. _to_svg (the .pipe(format='svg') shellout helper)
  is gone.
• main.py: the diagram(...) mkdocs-macro emits
  <figure class="qs-diagram"><script type="text/x-graphviz">DOT</script></figure>
  for every diagram. The figure wrapper keeps the existing
  qs-lightbox.js click-to-zoom working unchanged.
• stylesheets/qs-graphviz-wasm.js: ~50-line client-side
  bootstrap. Finds every <script type="text/x-graphviz"> block
  on page load, dynamically imports @hpcc-js/wasm-graphviz 1.x
  from jsDelivr (+esm), runs g.dot(source) against each, and
  replaces the script tag with the rendered SVG.
• .github/workflows/{ci,release,pages}.yml: 5 instances of
  apt-get install -y graphviz removed.
• pyproject.toml: graphviz>=0.20 Python lib stays as a
  [docs] dep — it's still constructing DOT source strings — but
  the comment explicitly notes the system binary is no longer
  required.
• tests/docs/test_handbook_diagrams.py: assertions updated
  to validate the DOT shape (digraph {...} syntax, expected
  node labels, expected edge counts) instead of SVG content.

Why this exists

Pre-Phase-T, every CI / Release / Pages job needed
graphviz/dot installed (a system package, not a Python wheel)
to build the docs site. New integrators hit the same wall on
their laptops. Phase S spiked two browser-rendered alternatives —
Mermaid + ELK and graphviz WASM — and concluded that
@hpcc-js/wasm-graphviz produces byte-identical layouts to the
build-time dot (it IS graphviz, just compiled to WASM and run
client-side). Mermaid + ELK lost on layout fidelity; the spike
findings live in PLAN.md § Phase S.

Compatibility

No CLI / Python API changes. The quicksight-gen docs apply
verb still emits a static site; the only difference is the site
no longer requires dot at build time. Diagrams render on
first page-load via the WASM bundle (~800kB, cached by the
browser after first hit).

Limitations + follow-ups

• Diagrams now require JavaScript to render; static-export
  consumers (PDF / printed docs) won't get them. Open follow-up
  if this becomes a real ask.
• qs-graphviz-wasm.js CDN-loads from jsDelivr. Vendoring the
  WASM lib into docs/_static/ for offline-friendly deploys is
  queued as PLAN.md T.7 — defer if jsDelivr's reliability is
  acceptable for the demo audience.