Freeze markdown without re-wrapping lines

[peterbjohnson]

source add converts a document with pandoc at its default --wrap=auto, so the frozen markdown is re-wrapped at 72 columns and inline maths ends up spanning lines. Now that draft validate runs the delimiter checks, every real sheet in the PHYS40002 folder fails with "newline inside an inline $ ... $" and "opening $$ must be followed by a newline": findings about pandoc's wrapping, not the document. The agent's replay sweep went from 15 built to 0 built on the relock because of them.

Freeze with --wrap=none so a paragraph is one line and inline maths never breaks; block line ranges still work, a paragraph simply spans one line. Then check the delimiter checks against the real export in tests/fixtures/exports: it holds 78 $$ and at least one inline span with a newline in it that Lambda Feedback renders, so a check that a real export fails is a check to loosen or drop, and say which in the PR. Done when the source and spec fixtures are re-frozen without wrapping, the questions-only PHYS40002 sheets validate with no delimiter findings, and every real export still passes the checks it passed before.

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Workbench ticket t44.