Keep the theme redraw from wiping a chart's x scale

Reaching Home from another page builds its charts in the same commit their
theme effect first fires in, with the readings already cached. uPlot ranges its
scales in a microtask, so `redraw()` re-set the x scale from the chart's own —
still empty — bounds before that ran, and the pending range taken from the data
was lost: axes without ticks, no lines, and no way back but the range control,
which rebuilds the chart. Redrawing without the paths is all a colour swap
needs and leaves the scales alone.

The cards also carried "Nothing has run yet." while the first readings were
still on their way; they now carry the skeleton the rest of Home uses.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01SKL7sUgNWhukDEz95vSMQv

frontend/src/components/Health/HealthActivity.tsx

@@ -100,11 +100,13 @@ function Chart({
   title,
   labels,
   plots,
+  pending,
   moment,
 }: {
   title: string
   labels: string[]
   plots: HistoryPoint[][]
+  pending: boolean
   moment: Moment
 }) {
   return (
@@ -127,6 +129,7 @@ function Chart({
         labels={labels}
         plots={plots}
         empty="Nothing has run yet."
+        pending={pending}
         onCursor={moment.onCursor}
         onSelect={moment.onSelect}
       />
@@ -205,7 +208,9 @@ export function HealthActivity({ range }: { range: Range }) {
   const runsAt = useMoment()
   const failuresAt = useMoment()
 
-  const { data: series } = useQuery(timeseriesQueryOptions(range))
+  const { data: series, isPending: seriesPending } = useQuery(
+    timeseriesQueryOptions(range),
+  )
   const { data: runs } = useQuery(runsQueryOptions(range))
   const { data: pinnedRuns } = useQuery(minuteRunsQueryOptions(runsAt.pinned))
   const { data: failures } = useQuery(failuresQueryOptions(range))
@@ -267,6 +272,7 @@ export function HealthActivity({ range }: { range: Range }) {
             at((point) => point.messages),
             at((point) => point.executions),
           ]}
+          pending={seriesPending}
           moment={runsAt}
         />
         <Chart
@@ -277,6 +283,7 @@ export function HealthActivity({ range }: { range: Range }) {
             at((point) => point.avg_ms),
             at((point) => point.avg_lag_ms),
           ]}
+          pending={seriesPending}
           moment={failuresAt}
         />
       </section>