Write a run's elapsed time once, in the duration formatter's units

The runs table drew when a run started and how long it took in two
notations ('56m ago | 55.5 min'), and for a run still going those are the
same reading twice. `dur` now steps past the minute into hours and days,
the ago reading is derived from it, and a running run writes only the
elapsed one.

frontend/src/lib/utils.check.ts

@@ -38,6 +38,8 @@ assert.equal(dur(0), "0 ms")
 assert.equal(dur(203.63), "204 ms")
 assert.equal(dur(1240), "1.24 s")
 assert.equal(dur(90_000), "1.5 min")
+assert.equal(dur(12_600_000), "3.5 h")
+assert.equal(dur(259_200_000), "3 d")
 
 // The plain window down to 0.01 ms, so a fast run keeps one unit across polls.
 assert.equal(dur(0.4), "0.4 ms")

frontend/src/lib/utils.ts

@@ -44,6 +44,8 @@ export function si(value: number, digits = 3): string {
 
 /** Floor, divisor and unit per step, largest first. */
 const DUR_STEPS: [number, number, string][] = [
+  [86_400_000, 86_400_000, "d"],
+  [3_600_000, 3_600_000, "h"],
   [60_000, 60_000, "min"],
   [1_000, 1_000, "s"],
   [0.01, 1, "ms"],
@@ -63,6 +65,9 @@ const DUR_STEPS: [number, number, string][] = [
  * window transposed onto units. That floor is deliberate: without it a tile
  * polled every ten seconds flips between "400 µs" and "1.2 ms", and a reading
  * that changes unit on every poll reads as broken rather than as fast.
+ *
+ * It keeps stepping past the minute into hours and days, so that an elapsed
+ * time is one notation wherever it is written — "3.5 h", never "210 min".
  */
 export function dur(ms: number, digits = 3): string {
   if (!Number.isFinite(ms)) return "--"