fix: keep empty list after blockquote as a sibling block

[spokodev]

Description

A blockquote immediately followed by a bare list marker line nests an empty list inside the blockquote instead of starting a sibling list.

Minimal repro

marked.parse('> foo\n-');

Expected (matches commonmark.js and markdown-it):

<blockquote>
<p>foo</p>
</blockquote>
<ul>
<li></li>
</ul>

Actual:

<blockquote>
<p>foo</p>
<ul>
<li></li>
</ul>
</blockquote>

Reproduces for -, *, +, 1., 1) and for multi line blockquotes (> foo\n> bar\n-). Non empty lists (> foo\n- bar) already behave correctly.

Root cause

The blockquote rule reuses the paragraph list interrupt clause:

 {0,3}(?:[*+-]|1[.)])[ \t]+[^ \t\n]

The trailing [ \t]+[^ \t\n] requires content after the marker, which is correct for a top level paragraph (an empty list cannot interrupt a paragraph). But the same clause also controls when a blockquote stops its lazy continuation. A bare marker line does not match it, so the marker line is lazily continued into the blockquote paragraph and then re lexed into a nested empty list.

Per CommonMark 0.31.2 (5.1 block quotes laziness, 5.2 list items) a list begun by a bare marker is a sibling block after the blockquote, not a lazy continuation of it. commonmark.js and markdown-it both produce the sibling.

Fix

Give the blockquote its own paragraph variant (blockquoteParagraph) whose list interrupt clause also matches a bare marker:

 {0,3}(?:[*+-]|1[.)])(?:[ \t]|\n|$)

The top level paragraph rule is left untouched, so foo\n- (setext heading), foo\n* and foo\n1. (no interruption) keep their current behavior. The change only affects when a blockquote ends.

Relation to #4003

#4003 also routes the blockquote rule through a blockquoteParagraph const, but for a different bug (#4002, non empty ordered lists with a start other than 1). It keeps the [ \t]+[^ \t\n] content requirement, so it does not fix the empty marker case verified here. The two changes touch the same region; I can rebase or fold the two interrupt clauses into one if a maintainer prefers a single edit.

Tests

• Added test/specs/new/empty_list_after_blockquote.{md,html} covering the bare unordered and bare ordered cases including a multi line blockquote.
• npm test green, including the CommonMark and GFM conformance specs (1745 spec assertions, 188 unit tests).

Contributor

• Test(s) exist to ensure functionality and minimize regression.
• no tests required for this PR.
• If submitting new feature, it has been documented in the appropriate places.

Committer

• CI is green (no forced merge required).
• Squash and Merge PR following conventional commit guidelines.

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