fix(viewer): fix monospace font rendering in pre/code blocks on Windows

[Kakarot30]

Summary

Fixes monospace font rendering in pre and code blocks on Windows
(Chrome & Edge). Closes #325.

Root Cause

Two issues combined to break monospace rendering on Windows:

1. Missing global rule — bare <pre> and <code> elements had no
   explicit font-family declaration, so they inherited the body's
   sans-serif stack (-apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif)
   instead of the monospace --mono variable.
2. Wrong font priority — the --mono CSS variable led with
   ui-monospace and SFMono-Regular, which are macOS-native aliases
   that don't resolve on Windows. The browser skipped all the way to
   the generic monospace fallback, which renders poorly.

Changes

internal/viewer/static/style.css

• Added a global code, pre rule immediately after the body block:

  code, pre {
      font-family: var(--mono);
  }

[CLAassistant]

All committers have signed the CLA.

[github-actions]

✅ OpenCodeReview: No comments generated. Looks good to me.

[lizhengfeng101]

LGTM