fix: clean up slow-load toast interval on component destroy (#8207)

The slowStreamIntervalId (which fires "Loading is taking a long time..."
toasts every 15s) was not cleared in onDestroy, causing it to keep
firing after navigating away from the runs page.

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

frontend/src/lib/components/runs/useJobsLoader.svelte.ts

@@ -666,6 +666,11 @@ export function useJobsLoader(args: () => UseJobLoaderArgs) {
 		if (intervalId) {
 			clearInterval(intervalId)
 		}
+		if (slowStreamIntervalId) {
+			clearInterval(slowStreamIntervalId)
+			slowStreamIntervalId = undefined
+		}
+		paramChangePromise?.cancel()
 	})
 	$effect(() => {
 		Object.keys(filters ?? {}).map((k) => filters?.[k as keyof RunsFilterInstance])