fix(make-pdf): stop URLs from swallowing smartypants placeholders

[marshaung]

Fixes #2084.

Root cause

make-pdf/src/smartypants.ts carves preserved zones in this order:

s = carve(s, CODE_ZONE_RE);
s = carve(s, TAG_RE);
s = carve(s, URL_RE);   // <- runs last

TAG_RE replaces each tag with a placeholder (\u0000SMARTPANTS_PRESERVED_N\u0000),
which contains no whitespace. URL_RE is /\bhttps?:\/\/\S+/g, so when a
URL sits flush against a tag, \S+ runs straight through the placeholder and
swallows it.

For a bare autolinked URL, marked emits:

<p>see <a href="https://ex.com">https://ex.com</a> ok</p>

which carves to PH_0see PH_1https://ex.comPH_2 okPH_3. URL_RE then matches
https://ex.comPH_2 and preserves that as a single entry. Restoration is a
single .replace() pass, so the nested PH_2 inside the restored text is
never re-scanned:

• the literal text SMARTPANTS_PRESERVED_2 renders into the PDF, and
• the </a> it stood for is gone — an unclosed anchor that bleeds
  link-blue through every following paragraph until some later </a> happens
  to close it.

**bold URL** swallows </a></strong> and leaks bold as well.
[text](https://…) is fine: the URL only lives inside an attribute, which
TAG_RE already carved as part of the whole tag.

Fix

Exclude the sentinel from URL_RE so carved placeholders survive:

-const URL_RE = /\bhttps?:\/\/\S+/g;
+const URL_RE = /\bhttps?:\/\/[^\s\u0000]+/g;

Tests

Three regression tests added to make-pdf/test/render.test.ts (bare URL, bold
URL, URL followed by punctuation). Verified they are load-bearing:

• reverting smartypants.ts alone → 3 fail
• with the fix → 69 pass / 0 fail (render.test.ts), 188 pass / 0 fail
  (full make-pdf/test/, 9 e2e skipped — no built binary in a fresh clone)

The existing does NOT touch URLs test missed this because its URL is followed
by a space rather than a tag.

Repro before the fix

pdftotext on a PDF generated from a bare URL, using the shipped 1.58.5.0
binary:

報價單網址是 https://quote.thinkrocket.com.twSMARTPANTS_PRESERVED_10 請點進去看。

with everything after that paragraph rendered blue.

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