feat(FN-4047): add responsive compact timestamps and mobile icon-only contr

Restored compact timestamp rendering in AgentDetailView and TaskDetailModal, added responsive timestamp layout for mobile and desktop, and added mobile icon-only stop/run controls to AgentDetailView, with new tests covering both components and a documentation note for the compact timestamp behavior.

Fusion-Task-Id: FN-4047

packages/dashboard/app/components/TaskDetailModal.css

@@ -157,14 +157,47 @@
 }
 
 .detail-timestamps {
+  display: inline-flex;
+  align-items: center;
+  flex-wrap: wrap;
+  gap: var(--space-xs);
   color: var(--text-dim);
   margin-top: var(--space-xs);
 }
 
+.detail-timestamp-item {
+  display: inline-flex;
+  align-items: baseline;
+  gap: var(--space-xs);
+}
+
+.detail-timestamp-label {
+  color: var(--text-muted);
+}
+
+.detail-timestamp-separator {
+  color: var(--text-dim);
+}
+
 @media (max-width: 768px) {
   .detail-provenance {
     align-items: flex-start;
   }
+
+  .detail-timestamps {
+    display: flex;
+    align-items: flex-start;
+    flex-direction: column;
+  }
+
+  .detail-timestamp-item {
+    align-items: flex-start;
+    flex-wrap: wrap;
+  }
+
+  .detail-timestamp-separator {
+    display: none;
+  }
 }
 
 .detail-meta-inline-controls {