Make the toner forecast an order, not a table

The report answers a purchasing question, and it was answering it in seven
columns, two tables and a rowspan. What someone actually needs from it is a
short list of what to buy.

So it opens with that list, grouped by part number with a quantity. Two
cartridges of the same part in different printers is a quantity of two, which
is the number an order needs and the one a per-printer table made the reader
count by hand. It covers what is empty plus what goes within a fortnight -
ordering only what is already empty means running empty. There is a copy
button, because it ends up pasted into a mail.

Below it the cartridges sit in urgency bands rather than in one long list
sorted by a number. The question is which pile a thing is in, and a pile that
is empty is worth seeing as empty. Everything past "empty" starts collapsed;
the order list above already covers the same ground in a tenth of the height.

The row is a cartridge now, not a printer, so it can carry its own part number,
its own level bar and its own countdown. Nesting supplies under a printer meant
opening a printer to find out whether anything on it needed doing.

Cartridges with no part mapped are counted on a single line rather than given
one each. They cannot be dropped, since that would quietly shorten the order,
and they cannot be ordered from here either - the job they represent is
mapping them, which is one job however many there are.

Bands and the order horizon are decided server-side, next to the arithmetic
that produces them, so a heading cannot disagree with what got added to the
list.

Checked against a fleet of 43 dev printers with real part mappings, driven by
a stub Zabbix - live Zabbix is not reachable from the dev box.

docs/api-inventory.json

@@ -2949,7 +2949,7 @@
     "path": "/api/printers/supplies/forecast",
     "auth": "jwt-optional",
     "params": "days (1-365, default 90)",
-    "purpose": "Days-to-empty per printer from Zabbix history, soonest first, with cartridge replacement counts; printers with no honest estimate are returned separately with the reason. available=false when Zabbix is unreachable",
+    "purpose": "One row per CARTRIDGE: days-to-empty from Zabbix history (hourly trends over a long window), soonest first, banded empty/soon/month/later, each with its part numbers and replacement count. Also returns orderlist - what to buy within horizondays, grouped by part number with a quantity. Cartridges with no honest estimate come back separately with the reason. available=false when Zabbix is unreachable",
     "example": "curl 'http://localhost:5001/api/printers/supplies/forecast?days=90'"
    }
   ]