Product variants across POS and stock

This release improves product variant management for retail businesses using options such as color and size.

• Variant identity: each variant can have its own unique reference, barcode and optional sale price. When no variant price is set, the parent product price is used automatically.
• POS: select color and size, scan a variant barcode, use variant prices, and withdraw stock from the exact variant. Variant data is also available in the offline catalog and printed receipts.
• Stock movements: manual entries, withdrawals, adjustments, inventory corrections and transfers can target a specific variant. Movement history displays the selected variant.
• Product page: variant references, barcodes and effective prices are visible, with direct label printing for each variant.
• Purchase PDFs: sender and recipient are now shown in the correct purchase flow order: supplier as sender and your company as recipient, with aligned contact details.
• Simple products and their existing workflows remain unchanged.