QA on dev showed .codeline spans wrap correctly but gutter .gutline spans
rendered inline (all at the same top), so numbers 6+ fell off with wrap on.
Add .gutter .gutline { display: block; } so each gutter number occupies its
own visual row, matching the one-number-per-visual-row contract of
paste-lines.js. Verified rendered output in a local build at 1400x900 and
375x812 with a long unbroken token on line 5 and wrap ON.
fen
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