fix: resolve double-encoded HTML entities in title and description

[Zerthick]

Description

Resolve double-encoded HTML entities (e.g. &, <, >) in RSS feed title and description fields.

MkDocs pre-escapes content, and then Jinja's |e filter escapes again, producing double-encoded entities. Using html.unescape() in Python before template rendering ensures |e performs a single correct escape.

Changes

• Add html_module.unescape() for title and description in plugin.py
• Add test fixture with special characters (& < >)
• Add test verifying no double-encoded entities in output

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Split from: #451

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💡 AI Contribution Level: 8 — Based on the VisiData AI contribution scale, this was an AI-assisted contribution where the AI performed the code splitting and PR creation with minimal human guidance.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.18%. Comparing base (1b5e630) to head (ada0a8d).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #456      +/-   ##
==========================================
+ Coverage   83.16%   83.18%   +0.02%     
==========================================
  Files          11       11              
  Lines         784      785       +1     
  Branches      133      133              
==========================================
+ Hits          652      653       +1     
  Misses         86       86              
  Partials       46       46              

Flag	Coverage Δ
unittests	83.18% <100.00%> (+0.02%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
mkdocs_rss_plugin/plugin.py	89.50% <100.00%> (+0.06%)	⬆️

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