feat: add intelligent import for CSV, Excel, and PDF files

Add IntelligentImportAugmentation with support for:
- CSV: auto-detection of encoding, delimiters, and field types
- Excel: multi-sheet extraction with metadata preservation
- PDF: text extraction, table detection, and metadata extraction

Features:
- Automatic format detection from file extension or content
- Intelligent type inference (string, number, boolean, date)
- Seamless integration with neural entity extraction
- Production-ready with 69 comprehensive tests

Dependencies added:
- xlsx@^0.18.5 for Excel parsing
- pdfjs-dist@^4.0.379 for PDF parsing
- csv-parse@^6.1.0 for CSV parsing
- chardet@^2.0.0 for encoding detection

Documentation:
- Updated README with import examples
- Updated API_REFERENCE with comprehensive import() docs
- Updated import-anything.md guide
- Added working example: import-excel-pdf-csv.ts
- Updated augmentations README

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