Escape dataset title in HTML serialization

[claudep]

Fixes CVE-2026-9318 - Stored XSS in tablib HTML Export via Unescaped Dataset Title

Many thanks to Katriel Moses and VulnCheck for the report.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.48%. Comparing base (27dffd5) to head (4a18004).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #668      +/-   ##
==========================================
+ Coverage   93.47%   93.48%   +0.01%     
==========================================
  Files          29       29              
  Lines        3308     3315       +7     
==========================================
+ Hits         3092     3099       +7     
  Misses        216      216              

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