docs: a technical introduction to the platform, as a LaTeX article

docs/blog/rarelens.tex builds a 10-page write-up covering the Nextflow DSL2
pipeline, the three execution backends behind one API call, the Argo and
ArgoCD track, Terraform, the external systems integrated, the ranking, the
benchmark and the model.

It is deliberately as much an account of what was wrong as of what works: the
components that scored evidence nobody had looked up, the missense AUROC that
fell from 0.872 to 0.500 once allele frequency was removed, the ontology walk
that silently dropped 399 terms, and the propagation change that measured
slightly worse than what it replaced and was kept anyway with the numbers
published.

Figures come from one headless-browser script. Screenshots are of the running
application; the six diagrams are hand-written HTML styled from the same
palette, rendered by the same script. Keeping both in one place is what stops
the article drifting from the system, and every number in a diagram has to be
changed deliberately.

.gitignore

@@ -19,4 +19,11 @@ data/*.vcf*
 data/*.tsv
 data/*.case.json
 data/*.zip
+# LaTeX build artefacts; the PDF itself is committed as the deliverable.
+docs/blog/*.aux
+docs/blog/*.log
+docs/blog/*.out
+docs/blog/preview-*.png
+docs/blog/diagram-sources/node_modules/
+docs/blog/diagram-sources/out/
 !data/README.md