fix(pptx): draw inhibition as inhibition, not as activation

[adamjohnwright]

An adversarial pass over the PowerPoint export shipped earlier today, checked against the diagram it claims to reproduce.

The defect that matters

The shape model had arrow: boolean, and the exporter turned every true into a filled triangle line end. The diagram draws four arrowheads, and three of them mean something a triangle does not:

edge	the diagram draws	the slide drew
production	filled triangle	filled triangle
catalysis	hollow circle	filled triangle
positive regulation	hollow triangle, green	filled triangle, navy
negative regulation	bar across the line, red	filled triangle

So a downloaded slide asserted the opposite of the pathway: inhibition read as activation.

OOXML line ends cannot express this — they are always filled, always the line's own colour, and there is no bar among triangle/stealth/diamond/oval/arrow. Arrowheads are now geometry the page computes and the exporter merely spells, the same division everything else here follows.

R-HSA-109606 exports 129 arrowheads: 84 filled triangles, 17 filled circles, 11 hollow circles, 9 hollow triangles, 8 bars. The 8 bars and 20 hollow heads match one-for-one the 8 red and 20 green marks in the site's own SVG.

Framed exports put shapes off the slide

Keeping a glyph that crosses the frame is right; keeping the parts that fall outside is not. An SVG has a viewBox and never draws them — a slide has nothing of the sort, so a connector spanning the diagram arrived as an object 31 inches off the side of an 11 inch slide.

Connectors are clipped per segment, so one crossing the frame twice returns as two runs rather than a line joining them through the middle. Glyph boxes are clipped with them, and an arrowhead is drawn only where the end it marks is in view. Both fixtures now assert the invariant that broke: every shape lies inside the extent the page declares. 0 shapes past the slide edge, from 17 of 40.

Smaller

• A text run keeps its alpha.
• A filled shape with no border no longer asks for a zero-width outline, which PowerPoint draws as a hairline — on a 16px arrowhead, most of the arrowhead.
• RENDER_CACHE_KEY → v5. v4 was published this morning and the output changed again.

Not defects, though they looked like ones

• The analysis overlay is carried in full. Every colour a run adds is exported; the missing-colour list is identical with and without a token.
• The 69 greys the SVG "draws" and the slide does not all have fill-opacity="0". The instrument that found them ignored opacity.

Still not carried

Node decorations drawn with background-image (a complex loses the band marking it as one), and rounded corners on round-segments edges. Both noted on #167.

Verified

Full preflight green. 55 unit assertions in tools/render/pptx.spec.mjs, driven by two payloads captured from the running page. Downloaded through Apache as a curator gets it: 765 shapes, 0 pictures, 0 line ends, 8 red and 20 green marks.

Refs #167