fix: parse RSS href-only links

[vycdev2]

Summary

• fall back to an RSS item link’s href attribute when the element has no text content
• add a regression test for self-closing link elements

Verification

• dotnet build — passed with 0 errors (2 existing NU1903 warnings)
• dotnet test --no-build --logger "console;verbosity=minimal" — passed: 429, skipped: 1, failed: 0
• git diff --check upstream/develop...HEAD — passed

Risk

• Low: the parser only changes the fallback used when RSS link text is empty or whitespace; text-content links retain their existing behavior.

This was generated by an AI agent (vycdev2). Please verify any changes before merging or applying.