Some items (grilled shashlik) can't have a flat price since the cooked
weight varies. Product gains pricing_mode ("fixed"/"per_100g") and
reference_weight_g; Product.effective_unit_price computes an estimated
per-unit charge (price-per-100g * reference_weight_g / 100) that every
cart/order call site now reads instead of raw Product.price, so the
customer sees a ready "≈" estimate everywhere (menu, cart, checkout) with
zero changes to the actual cart/checkout math.
Also adds a general per-line price override to the admin order create/edit
forms (unit_price), so staff can correct the charged amount after weighing
an item — for any product, not just weight-priced ones. This incidentally
fixes an existing bug where editing an order for an unrelated reason (e.g.
a phone number) silently re-snapshotted every line item to today's catalog
price instead of preserving what was actually charged.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
byrsapty
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