Fix PDF build: render plantweb diagrams as PNG for non-HTML builders

plantweb defaults to SVG format, which pdflatex cannot include, causing
a fatal 'Unknown graphics extension: .svg' error in the LaTeX build.

Sphinx adds the builder name to 'tags' before executing conf.py, so we
can override plantweb's defaults cache to use PNG for any non-HTML
builder (latex, man, texinfo, etc.). HTML builds continue to use SVG
for crisp vector output.

https://claude.ai/code/session_014hVQ5UrK1B4N9ar4UfYpm4

Author: claude

doc/conf.py

@@ -20,6 +20,14 @@
 # that regardless of FORCE_COLOR, and dfetch's own Rich console respects it too.
 os.environ["NO_COLOR"] = "1"
 
+# plantweb renders PlantUML diagrams as SVG by default, which pdflatex cannot
+# include. Override to PNG for all non-HTML builders (e.g. LaTeX/PDF).
+if not tags.has("html"):  # type: ignore[name-defined]  # noqa: F821
+    import plantweb.defaults as _plantweb_defaults
+    _pd = _plantweb_defaults.read_defaults()
+    _pd["format"] = "png"
+    _plantweb_defaults.read_defaults.cache = _pd
+
 # -- General configuration ------------------------------------------------
 
 ext_path = os.path.abspath(os.path.join(os.path.dirname(__file__), "_ext"))