- Add processDocx and processExcel in ContentProcessingService (Apache POI)
- Extract text from Word (paragraphs, tables) and Excel (sheets, cells)
- Add DOCX and EXCEL to ContentType enum and ContentTypeDetector
- Replace FileValidationUtil S3 dependency with standalone validation
- Add allowed extensions (doc, docx, xls, xlsx, csv) and 100MB limit
- Add pdfbox and poi-ooxml dependencies.