🔧 Clean up display of highlighted search results

[noeddl]

This PR demonstrates some ideas for improving the presentation of search results:

• Use a delimiter ([...]) to make the boundaries between text snippets clearer
• Properly render HTML entities (e.g., " → ")
• Treat clusters of whitespace (including multiple line breaks) as boundaries for references to reduce noise and avoid confusion caused by whitespace collapsing into a single space
• Remove duplicate or near-duplicate references

Before:

After:

This is open for discussion. At the moment, I’ve hacked it directly into froide for demonstration purposes, but it would likely be better to implement it in a way that allows configuration from the main project.