Bulk-import articles (invoice items) from a CSV/Excel spreadsheet

Imports many articles/products at once from an uploaded spreadsheet (CSV or Excel). The pipeline auto-detects the file's structure, then uses Claude to map each row onto the invoice-item model (name, price, units, vatRate). Rows with no usable name and rows the model flags as non-article are skipped, and duplicates are skipped by matching the normalised name against the user's existing items (and earlier rows in the same file). Surviving items are written in batches.