fix(webapp): drop a skipped query's stale rows and failure

The empty-query short circuit returned before the block that resets rows and the
failure flag on a new query signature, so a caller that stopped asking kept the
last answer. On the Queues page that meant a readout which failed once on a short
range stayed hidden after widening to a range where the readout is skipped
entirely and the headline comes from the chart's own successful rows — the number
would have been missing for the rest of the session.

Reproduced by failing only the p95 readout on a 1-hour range (headline gone as
designed) and then widening to 7 days: the headline now returns at 58.3s.

Clearing rows as well as the flag, since no query means no data, and leaving
another query's rows behind is the same trap the reset below guards against.

Author: ericallam

apps/webapp/app/hooks/useMetricResourceQuery.ts

@@ -51,7 +51,11 @@ function cacheSet(key: string, rows: MetricResourceRow[]) {
  * back-navigation to the queues list) shows its last data immediately and revalidates in the
  * background rather than flashing a loading skeleton.
  */
-/** An empty query means the caller has nothing to ask for, so no request is made. */
+/**
+ * An empty query means the caller has nothing to ask for, so no request is made and any rows or
+ * failure left by a previous query are dropped — a caller that stops asking must not keep reading
+ * the last answer, or a stale failure would outlive the query that caused it.
+ */
 export function useMetricResourceQuery(query: string, opts: MetricResourceQueryOptions) {
   const {
     organizationId,
@@ -103,6 +107,10 @@ export function useMetricResourceQuery(query: string, opts: MetricResourceQueryO
 
   const load = useCallback(() => {
     if (!query) {
+      abortRef.current?.abort();
+      loadedKeyRef.current = cacheKey;
+      setRows(null);
+      setFailed(false);
       setIsLoading(false);
       return;
     }