Only zero is empty, and the last day is worth reading

Two separate floors were collapsing a live cartridge into a spent one, and
removing either alone changes nothing.

EMPTY_LEVEL was 5, so everything at or below 5% was assigned daysleft 0
outright. The reasoning was that a printer at 1% is out of toner as far as
anyone standing at it is concerned. But the row exists to say how long is
left, and 2% draining a point a day has two days in it. Flooring put that
cartridge beside ones that genuinely are empty with no way back to the
difference. It is 0 now: empty means empty.

int(level / rate) then truncated the division, so anything under a full day
arrived as 0 whatever the floor did - a cartridge with six hours in it was
indistinguishable from one with nothing, and the band read it as empty.
daysleft is fractional now, rounded to two places, which is about a quarter of
an hour: finer than the estimate deserves, but it costs nothing and keeps the
ordering of two nearly-spent cartridges meaningful.

daysText reads in whatever unit carries meaning: "6 hours", "1 hour", "29 min",
"4 days". Below an hour it goes to minutes with a floor of one, because
rounding hours would land back on "empty" - the same bug one rung down.

BEHAVIOUR CHANGE worth knowing: a cartridge at 1-5% with NO history used to get
daysleft 0 from the floor and land on the order list. A rate needs two
readings; with none there is nothing to divide, and the old answer was right by
accident - it said "empty" about a level nobody had watched move. It now
reports 'no history' and shows under "No estimate yet". This reaches only
printers newly added to Zabbix; anything that got to 3% the ordinary way has
the history to forecast from.

Five existing tests pinned the old rule. They recorded a real decision, so they
are rewritten to the new one rather than deleted. One of them was passing for
the wrong reason: its series (2.0, 1.7, 1.4, 1.1) drops 0.9, under
MIN_DROP_FOR_ESTIMATE, so it never had a rate at all and only passed because
the floor short-circuited ahead of the rate check. It now uses a real 20-day
drop at a tenth of a point a day and asserts the ten days its docstring always
described.

The forecast fixture's black cartridge moves from 1% to 0% so the empty band
keeps its API-level coverage, and a magenta at 3% covers hours-left end to end.

plugins/printers/frontend/views/TonerForecast.vue

@@ -293,11 +293,32 @@ function barWidth(cartridge) {
   return Math.max(0, Math.min(100, level)) + '%'
 }
 
+// daysleft is fractional, so the last day of a cartridge's life is readable
+// instead of collapsing to "empty". Only an actual zero is empty; anything above
+// it has time left and the row says how much, in whatever unit carries meaning.
+const HOURS_PER_DAY = 24
+const MINUTES_PER_HOUR = 60
+
 function daysText(cartridge) {
-  if (cartridge.daysleft == null) return '-'
-  if (cartridge.daysleft === 0) return 'empty'
-  if (cartridge.daysleft === 1) return '1 day'
-  return cartridge.daysleft + ' days'
+  const days = cartridge.daysleft
+  if (days == null) return '-'
+  if (days <= 0) return 'empty'
+
+  if (days < 1) {
+    const hours = days * HOURS_PER_DAY
+    // Under an hour, hours would round to 0 and read as empty again.
+    if (hours < 1) {
+      const minutes = Math.max(1, Math.round(hours * MINUTES_PER_HOUR))
+      return `${minutes} min`
+    }
+    const rounded = Math.round(hours)
+    return rounded === 1 ? '1 hour' : `${rounded} hours`
+  }
+
+  // Whole days from here. The estimate is not precise enough for "3.7 days" to
+  // mean more than "about 4", and a column of decimals is harder to scan.
+  const rounded = Math.round(days)
+  return rounded === 1 ? '1 day' : `${rounded} days`
 }
 
 function orderKey(item) {