Surface matching subjects in search results

[cdrini]

First piece of #9898 pulled out, so we can monitoring the impact of highlighting on performance and merge a good chunk of that code in first.

Adds ability to show matching subjects in book search results to:

• Make it easier for people who are making more generic queries to explore
• Provide more context as to why a book is appearing

Technical

Testing

Screenshot

https://testing.openlibrary.org/search?q=horror+short+stories&mode=everything&sort=trending

Stakeholders

[Copilot]

Pull Request Overview

Surfaces matching subjects in book search results by enabling Solr highlighting and rendering highlighted subject tags in the UI.

• Plumbs a highlight flag through the search pipeline, adds SearchResponse.highlighting, and cleans highlight snippets (stopword filtering and sorting).
• Renders highlighted subject tags in SearchResultsWork and styles them with new CSS.
• Adds a reusable subject_name_to_key helper and adopts it in SubjectTags.

Reviewed Changes

Copilot reviewed 11 out of 11 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
static/css/components/search-result-item.less	Adds styles for highlighted subject chips and emphasis styling.
openlibrary/templates/work_search.html	Passes per-work Solr highlighting into SearchResultsWork.
openlibrary/plugins/worksearch/schemes/works.py	Adds highlight support to Solr params for works (hl.* settings).
openlibrary/plugins/worksearch/schemes/subjects.py	Aligns q_to_solr_params signature to accept highlight flag.
openlibrary/plugins/worksearch/schemes/lists.py	Aligns q_to_solr_params signature to accept highlight flag.
openlibrary/plugins/worksearch/schemes/authors.py	Aligns q_to_solr_params signature to accept highlight flag.
openlibrary/plugins/worksearch/schemes/init.py	Base scheme q_to_solr_params signature updated with highlight flag.
openlibrary/plugins/worksearch/code.py	Implements highlighting plumbing, stopword loading, highlight cleaning, and response shaping.
openlibrary/plugins/upstream/utils.py	Introduces subject_name_to_key helper (DRYs subject URL construction).
openlibrary/macros/SubjectTags.html	Switches to subject_name_to_key for subject links.
openlibrary/macros/SearchResultsWork.html	Displays highlighted subjects under results and links to subject pages.

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[cdrini]

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