Replace plain recursive chunker with legal-aware chunking that:
- Detects legal section headers (§, Art., Section, Chapter, Annex)
- Adds section context prefix to every chunk
- Splits on paragraph boundaries then sentence boundaries
- Protects DE + EN abbreviations (80+ patterns) from false splits
- Supports language detection for locale-specific processing
- Force-splits overlong sentences at word boundaries
The old plain_recursive API option is removed — all non-semantic
strategies now route through chunk_text_legal().
Includes 40 tests covering header detection, abbreviation protection,
sentence splitting, and legal chunking behavior.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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