[#7] Strip Sphinx headerlink from indexed content

[joubu]

Description

Remove .headerlink anchor elements before extracting text from HTML headings and content blocks. This prevents Sphinx permalink icons () from polluting hierarchy titles and search results in Typesense.

Related Issue

Fixes #7

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update
• Code refactoring (no functional changes)
• CI/CD changes
• Dependencies update

Checklist

• I have performed a self-review of my code
• I have added/updated tests that prove my fix is effective or my feature works
• I have updated the documentation accordingly
• I have added a changelog entry (if applicable)
• All CI checks pass
• My changes generate no new warnings

Testing

I am not confident with the suggestion as it sounds too specific. A better approach would be to have the selectors defined in the config.
However I am not even sure it's correct: the class is not on the header
<h1>Acquisitions<a class="headerlink" href="#acquisitions" title="Link to this heading"></a></h1>