feat(FN-2632): pin return-to-live control to bottom-right

- Update .agent-log-return-to-live to anchor on the right edge while staying sticky at the bottom
- Switch the control container to flex with fit-content width to keep compact button sizing
- Add mobile-specific right offset so spacing stays consistent at smaller breakpoints

packages/dashboard/app/components/TaskDetailModal.css

@@ -450,9 +450,11 @@
 
 .agent-log-return-to-live {
   position: sticky;
+  right: var(--space-md);
   bottom: var(--space-md);
+  width: fit-content;
   margin-left: auto;
-  display: inline-flex;
+  display: flex;
   align-items: center;
   gap: var(--space-xs);
   padding: var(--space-xs) var(--space-sm);
@@ -1512,6 +1514,7 @@
   }
 
   .agent-log-return-to-live {
+    right: var(--space-sm);
     bottom: var(--space-sm);
   }
 }