refactor(agents): replace unimplemented mutation with simple function

Replace the placeholder mutation implementation in useUpdateAgent hook with a simpler function that shows a toast notification. This removes the unnecessary query client usage for an unimplemented feature.

src/renderer/src/hooks/agents/useUpdateAgent.ts

@@ -1,18 +1,7 @@
-import { AgentEntity } from '@renderer/types'
-import { useMutation, useQueryClient } from '@tanstack/react-query'
-
 export const useUpdateAgent = () => {
-  const qc = useQueryClient()
-
-  // TODO: use api
-  return useMutation({
-    mutationFn: async (agentUpdate: Partial<AgentEntity> & { id: string }) => {
-      throw new Error(`useUpdateAgent mutationFn not implemented for agent ${agentUpdate.id}`)
-    },
-    onSuccess: (updated: AgentEntity) => {
-      qc.setQueryData<AgentEntity[]>(['todos'], (old) =>
-        old ? old.map((t) => (t.id === updated.id ? updated : t)) : []
-      )
+  return {
+    updateAgent: () => {
+      window.toast.info('Not implemented')
     }
-  })
+  }
 }