* Studio: fix link, currency and indentation edge cases in LaTeX rendering
Follow-up to #6914. Three fixes to studio/frontend/src/lib/latex.ts:
- Skip reference-link definition URLs ([id]: url) during delimiter
conversion, so escaped parens in such URLs are not rewritten as math.
- Preserve the opener line's indentation when emitting a display $$ block,
so a \[...\] inside a list item stays part of the list.
- Stop a currency amount from pairing with a converted span's opening $,
which swallowed the price into math (for example $5 + x \(y\)).
* Exclude GFM footnote definitions from the reference-URL skip
A footnote definition like [^1]: \(x\) had its body treated as a link
destination, so leading math was left literal. Skip [^...] labels.
* Merge overlapping link destination regions
A reference-def token can nest inline-link spans (for example
[1]: http://h/[a](b)/foo\(x\)), so the combined spans could overlap and
isInRegion's binary search missed the outer one, rewriting the URL. Merge
overlapping spans before the search.
* Guard lineStart when the display opener is at index 0
Behavior is unchanged (lastIndexOf clamps a negative fromIndex to 0), but
the explicit guard avoids relying on that implicit clamp.
* Scope to indentation and currency fixes
Drop the reference-link URL protection added earlier. It guards a case
models effectively never emit (escaped parens in a reference-style URL),
and approximating CommonMark reference definitions with a regex needs
open-ended special-casing. Keep the two high-value fixes: preserve display
math indentation (including multi-line bodies) inside a list item, and stop
a currency amount from pairing with a converted span's opening dollar sign.
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