IB-WP-0016-T01: spine-aware EPUB3 intake

Parse META-INF/container.xml and the OPF package document, then iterate
documents in spine reading order instead of archive-name sort. Classify
each spine item (body, cover, nav, toc, header, footer, notes, license,
auxiliary) and exclude non-body sections by default; include_non_body=True
opts them back in for inspection. Capture OPF book metadata (title,
creator, language, subjects, rights, identifier, source_url, modified)
onto every chunk and propagate it through source artifact provenance.
Preserve the legacy zip-without-OPF fallback for malformed EPUBs.

Real Lefevre EPUB now yields 148 body chunks in spine order (was 155
mixed, archive-sorted) with cover=1, header=1, footer=4 detected and
dropped. 78 tests pass.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/infospace_bench/generator.py

@@ -258,6 +258,9 @@ def _register_source_chunks(root: Path, chunks: list[SourceChunk]) -> None:
                 "chunk_count": chunk.chunk_count,
                 "imported_at": chunk.imported_at,
                 "extractor_version": chunk.extractor_version,
+                "section_role": chunk.section_role,
+                "spine_index": chunk.spine_index,
+                "book_metadata": dict(chunk.book_metadata),
             },
         )