Closes#902.
Two gaps in the structured ZIM extraction path:
1. NON_CONTENT_HEADING_PATTERNS was only used by the structure heuristic to
count meaningful sections, never at section-emit time. Sections under
"See also" / "References" / "External links" / etc. were still chunked and
embedded. They're now flagged when the heading opens and dropped.
2. <table> elements were run through cheerio's `.text()`, concatenating every
cell with no separators ("AgeDoseAdult500mg") into unsearchable word salad.
New tableToText() joins cells with " | " and rows with newlines so
row/column structure survives into the chunk.
Refactor: moved extractStructuredContent out of ZIMExtractionService into a
pure, cheerio-only util (app/utils/zim_html.ts) so it can be unit-tested
without the native @openzim/libzim binding. Service delegates to it; behavior
is otherwise unchanged. Adds tests/unit/zim_html.spec.ts (6 tests).
Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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