fix(activity): clamp agent summary to 3 lines

Showing the full message made tall rows for chatty agents. Cap at 3
lines (line-clamp-3) — long enough to convey what happened, short
enough that rows stay scannable. Users open the workspace if they want
the full transcript.

Co-authored-by: Orca <help@stably.ai>

src/renderer/src/components/activity/ActivityPrototypePage.tsx

@@ -391,7 +391,7 @@ function AgentEventRow({
             </TooltipContent>
           </Tooltip>
         </div>
-        <div className="mt-0.5 break-words whitespace-pre-wrap text-sm text-muted-foreground">
+        <div className="mt-0.5 line-clamp-3 break-words whitespace-pre-wrap text-sm text-muted-foreground">
           {agentSummary(event)}
         </div>
         <div className="mt-1.5 flex min-w-0 flex-wrap items-center gap-x-2 gap-y-1 text-[11px] text-muted-foreground">