S3.5 — Dev environment and docs refresh

#task #oxmpl #oxmpl/epic #oxmpl/story/size-S #oxmpl/sprint/002

Intent

Local tools are a year stale (flake.lock 2025-10: maturin 1.8.7, wasm-pack 0.13.1, mdbook 0.4.52). Align the dev shell with CI and confirm the docs survive mdBook 0.5's breaking changes (we override theme/head.hbs for MathJax).

Acceptance criteria

nix flake update; dev shell provides maturin ≥ 1.15, wasm-pack 0.15, mdbook 0.5, node ≥ 22.12
pre-commit-hooks rev v6.0.0; pre-commit run --all-files clean (incl. clippy -D warnings on the newer nightly)
mdBook 0.5 render checked by eye: MathJax renders on python_api / js_api / concepts pages
Install docs state Python ≥ 3.11, Rust ≥ 1.85, Node ≥ 22.12
Migration notes drafted for the release: rand trait renames, Python floor

Tasks

Update flake.lock, requirements.txt pins, .pre-commit-config.yaml
Fix any new clippy lints
Docs edits

Source

Agreed in the senior-engineer grilling session 2026-10-08 (decisions in repo docs/planning/adr/0003-motion-validation.md, glossary in CONTEXT.md; toolchain research briefs in the same session).