FIX: fixes for PDF builder

[mmcky]

This PR is trying to fix the broken pdf builds on publish

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[mmcky]

• for some reason the PDF builder is not triggering a failure condition -- but it is failing on the pdf build due to unsupported unicode characters in code generated outputs.

[mmcky]

• migrate to use local github actions instance and then diagnose issue to see if latex issue is due to EC2 environment
• fixes or add support for new unicode characters in pdf

[mmcky]

Closing as superseded, with one line carried forward.

The markdown half is already on main. 230e90c refreshed bayes_nonconj.md from lecture-python.myst, dropping the raw <u> HTML and the paramter typo this PR fixed, and going further by wrapping the sentence in a {note} admonition. That is also the sole merge conflict here — the branch conflicts on the exact line it was opened to fix, and main's resolution is the better one.

The -n addition was a genuine fix and has been carried into #54. ci.yml's PDF build was the only jb build in that file without -n, while publish.yml runs the same pdflatex build with -n -W. That gap let a bad cross-reference or missing citation pass the PR check and then fail the tag-only publish build.

Not carried forward: the build-folder upload step, which lacks the if: failure() guard its three siblings have and so would upload the whole _build tree on every run.

One thing this closure does not resolve. I could not confirm whether the original unicode-in-PDF failure still reproduces, because ci.yml currently dies at the pip install step and never reaches the PDF build. There is no latex preamble in lectures/_config.yml, which suggests the root cause was never addressed. If it is still live it deserves a fresh issue against the current RunsOn environment rather than reviving this branch, whose assumptions (EC2, pre-refresh bayes_nonconj.md) no longer hold.