Add missing spec-compliant methods and fields while keeping the working
implementation that correctly handles the complex Excel structure.
Changes:
- Add public isOrderRow() method to detect order title rows
- Add public extractOrderNumber() method to extract order numbers
- Add public parseMaterialRow() method for spec compliance
- Rename internal parseMaterialRow() to parseMaterialRowInternal()
- Add missing pendingQty field to DiscreteMaterialPlan type
All tests pass (23/23).
Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>
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