feat!: emit list tables and escape description prose for Quarto 2

[edavidaja]

Quarto 2 rejects markdown constructs the extension currently emits. This makes
the generated .qmd render on both Quarto 1.9+ and Quarto 2.

Stacked on #27, which moves the pre-render script to Node.

Grid tables become list tables

Quarto 2 dropped Pandoc grid tables. List tables render on both, so the
extension emits them unconditionally rather than carrying two renderers.

Column widths are carried over rather than recomputed: each fraction is
derived from the character width the grid emitter would have given the column,
so rendered proportions are unchanged. Quarto normalizes them to percentages.

This also removes a constraint. Grid cells had to be in final form before
layout, because changing a cell's length afterward broke the alignment Pandoc
reads the table from — that is what motivated rewriting operationId refs
before rendering (#25). The rewrite is still needed so every sink sees the
same text, but it is no longer load-bearing for layout, and the tests no
longer assert a width invariant that cannot break.

Description prose is escaped

Descriptions are CommonMark written for arbitrary renderers, so they carry
constructs Quarto reads as markup. Quarto 2 hard-errors on the first two and
warns on the third, once per element per page.

In the spec	In the output
[start, start+interval)	\[start, start+interval)
/v1/users/{guid}/keys	/v1/users/\{guid\}/keys
<a href="/x">bundle</a>	```{=html}bundle`{=html}``

Every rewrite skips inline code spans and fenced code blocks, where braces and
angle brackets already render verbatim and a backslash or backtick would
become literal output. A path written as GET /v1/users/{guid}/keys
keeps its braces.

The HTML pass runs first: it wraps each tag in backticks, so the bracket pass
then treats those as code spans and leaves a [ inside an attribute
(href="/x?a[0]=1") alone. The tag pattern requires a well-formed name and
angle-bracket-free attributes, which leaves a < b and CommonMark autolinks
alone — wrapping an autolink would break the link Quarto otherwise makes of it.

All three render identically to the unescaped text, so none of this is
conditional on the Quarto version.

Value formatting

Empty strings format as "" rather than an empty code span, which renders as
nothing at all. Enum members go through the same formatter as defaults and
examples, so null and non-string members format consistently.

Compatibility

quarto-required rises from >=1.6.0 to >=1.9.0. List-table support
landed in 1.9; 1.6–1.8 render list tables as bullet lists, silently. Verified
across 1.6.43, 1.7.34, 1.8.27, 1.9.30 and 1.9.32. The escaping and value
formatting are safe on every version.

The bound is enforced exactly where it needs to be. Quarto 1 refuses an
extension whose quarto-required it does not satisfy; Quarto 2 ignores the
field entirely, and loads the extension whatever the bound says (tested at
>=1.6.0, >=1.9.0, >=2.0.0 and >=99.0.0 on q2 0.25.0 — no error, no
warning, contributed filter ran every time). So the guard blocks the 1.6–1.8
users who would get bullet lists, and is inert for q2 users, who always have
list tables. Nothing on q2 needs guarding.

The version bump to 0.5.0 covers this PR and #27 together, as one release.

Verification

97 tests (16 new), typecheck clean, and quarto render on the example. A
probe spec exercising every escaped construct renders correctly: brackets and
braces come through as literal text, the <a> becomes a real link with
a[0]=1 intact in its query string, <admin@example.com> becomes a mailto
link rather than being wrapped, and Default: "" / Enum: "" are visible.

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