Move scroll-to-bottom button to issue detail and run pages

Removed the scroll-to-bottom button from IssuesList (wrong location)
and created a shared ScrollToBottom component. Added it to IssueDetail
and RunDetail pages. On mobile, the button sits above the bottom nav
to avoid overlap.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

ui/src/pages/AgentDetail.tsx

@@ -24,6 +24,7 @@ import { CopyText } from "../components/CopyText";
 import { EntityRow } from "../components/EntityRow";
 import { Identity } from "../components/Identity";
 import { PageSkeleton } from "../components/PageSkeleton";
+import { ScrollToBottom } from "../components/ScrollToBottom";
 import { formatCents, formatDate, relativeTime, formatTokens } from "../lib/utils";
 import { cn } from "../lib/utils";
 import { Button } from "@/components/ui/button";
@@ -1747,6 +1748,7 @@ function RunDetail({ run, agentRouteId, adapterType }: { run: HeartbeatRun; agen
 
       {/* Log viewer */}
       <LogViewer run={run} adapterType={adapterType} />
+      <ScrollToBottom />
     </div>
   );
 }