[codex] Fix exported document centering

[ThisIs-Developer]

Summary

• Fixes HTML not centered #152 by making exported HTML fit its rendered Markdown content before settling the page width.
• Removes the exported document body's default browser margin so the centered article aligns predictably.
• Applies the same content-fit measurement before PDF capture so wide custom layouts are included instead of clipped.

Root Cause

The live preview uses the available preview pane width, but exported HTML forced .markdown-body into a GitHub-style max-width: 980px container with the browser's default body margin still applied. Markdown documents that include wider custom layouts, such as a two-column CSS grid, could overflow that fixed article box. The HTML then appeared offset, and the PDF capture used the narrower box, leaving the overflowing right side outside the page.

User Impact

Wide exported documents now stay centered as a single document surface. If content needs more than the default 980px article width, the export widens the article to fit it; PDF export then captures that full width and scales it onto the page.

Validation

• node --check script.js
• git diff --check
• Local browser layout check against the provided exported sample document with the new fitting behavior.

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Project	Deployment	Actions	Updated (UTC)
markdown-viwer	Ready	Preview, Comment	Jun 4, 2026 8:12pm