Orders (F3) in IMS2 — business logic for the user

Orders track what has been ordered from us: an external customer wants
a certain quantity of items, we may not have that full quantity in stock
yet, and we ship it gradually, tracking "ordered / shipped".

1. Structure

• Order (header) — customer, period (a start and end date), comment.
• Line — any item from the reference (raw material or finished product
  — no restriction), with fields:
• Ordered — how much the customer wants.
• Shipped — how much has actually been sent so far,
  accumulates as shipments happen. Starts at 0.
• Remaining — computed on screen as "Ordered minus Shipped", not
  stored separately.

2. How shipping happens

Orders does not ship from the Orders screen itself — it's a reference
list of "what's owed". Actual shipping happens through a normal expenditure
document (the "Order" button on the expenditure form) — you pick an open
order line, enter the quantity to ship, and process the document as usual.

When the document is processed the system automatically:
- adds the shipped quantity to the line's shipped total;
- if the shipped total reaches what was ordered — the line closes automatically;
- if all lines of the order are closed — the order closes automatically.

No separate "close" click is needed if shipping goes through in full.

3. Manual close

The Close Order button forcibly closes an order even if something is
not yet fully shipped (e.g. the customer canceled the remainder). This is
a separate action from auto-close-on-shipment — used only when the order
needs to be closed earlier than it's actually fulfilled.

4. Editing restrictions

• The ordered quantity of a line cannot be reduced below what's already
  shipped.
• A line cannot be deleted if anything has already been shipped against it.
• The whole order cannot be deleted if at least one line has shipments.

This protects against accidentally losing history — if something has
already left the warehouse against a line, its data can't be erased, only
closed.

5. Notifications

Closing a line/order is logged in the general event log (Tools → Events →
the Events tab) — you can see there when and what closed. These
notifications do not pop up on the main-screen panel — that panel only
shows stock shortages (see docs/en/business-logic/events_en.md); order
closures are intentionally left out to avoid distracting from the main
signal. The full order history is always available in the log itself.