Recover from a dead session, and report a node problem once

An expired or orphaned session left the app on a half-rendered page instead of
the login screen: a properly signed token naming a user who no longer exists
answered 404, which the client does not treat as an authentication failure. All
failures in get_current_user are 401 now, and the client stops retrying them,
so a dead session goes straight back to the login screen.

- Clicking an edge names the two nodes it runs between, not just the message.
- A node with a problem shows one badge carrying the whole explanation, rather
  than a corner badge and a status dot saying the same thing twice. The dot is
  back to what it is good at: whether the node ran.
- The sidebar's collapse control sits in the sidebar, where a phone still finds
  one in the chrome because there is no sidebar on screen to hold it.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016WzrvW7rjQbynnhF6pxh6i

frontend/src/components/Flow/FlowEditor.tsx

@@ -166,7 +166,6 @@ function FlowEditorInner({ flowName }: { flowName: string }) {
             flow: flowName,
             typeLabel:
               typeLabels.get(definition?.type ?? "") ?? definition?.type ?? "",
-            issues: nodeIssues.length,
             issueText: nodeIssues.join("\n"),
           } satisfies FlowNodeData,
         }
@@ -413,8 +412,14 @@ function FlowEditorInner({ flowName }: { flowName: string }) {
           setInspected(null)
         }}
         onEdgeClick={(event, edge) => {
+          const label = (id: string) => {
+            const node = definitions.find((entry) => entry.id === id)
+            return node?.title || node?.id || id
+          }
           setInspected({
             message: (edge.data as { message: string }).message,
+            from: label(edge.source),
+            to: label(edge.target),
             x: event.clientX,
             y: event.clientY,
           })