story-kit: merge 271_story_show_assigned_agent_in_expanded_work_item_view

Adds assigned agent display to the expanded work item detail panel.
Resolved conflicts by keeping master versions of bot.rs (permission
handling), ChatInput.tsx, and fs.rs. Removed duplicate list_project_files
endpoint and tests from io.rs.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/components/WorkItemDetailPanel.tsx

@@ -113,6 +113,7 @@ export function WorkItemDetailPanel({
 	const [content, setContent] = useState<string | null>(null);
 	const [stage, setStage] = useState<string>("");
 	const [name, setName] = useState<string | null>(null);
+	const [assignedAgent, setAssignedAgent] = useState<string | null>(null);
 	const [loading, setLoading] = useState(true);
 	const [error, setError] = useState<string | null>(null);
 	const [agentInfo, setAgentInfo] = useState<AgentInfo | null>(null);
@@ -133,6 +134,7 @@ export function WorkItemDetailPanel({
 				setContent(data.content);
 				setStage(data.stage);
 				setName(data.name);
+				setAssignedAgent(data.agent);
 			})
 			.catch((err: unknown) => {
 				setError(err instanceof Error ? err.message : "Failed to load content");
@@ -278,6 +280,14 @@ export function WorkItemDetailPanel({
 							{stageLabel}
 						</div>
 					)}
+					{assignedAgent ? (
+						<div
+							data-testid="detail-panel-assigned-agent"
+							style={{ fontSize: "0.75em", color: "#888" }}
+						>
+							Agent: {assignedAgent}
+						</div>
+					) : null}
 				</div>
 				<button
 					type="button"