fix(useSessions): correct session fetching logic to use API call

Previously the getSession hook was only searching local data. Now it properly fetches from the API and updates the cache. This ensures data consistency when sessions are modified elsewhere.

src/renderer/src/hooks/agents/useSessions.ts

@@ -30,9 +30,11 @@ export const useSessions = (agent: AgentEntity) => {
   // TODO: including messages field
   const getSession = useCallback(
     async (id: string) => {
-      return data?.find((session) => session.id === id)
+      const result = await client.getSession(agent.id, id)
+      mutate((prev) => prev?.map((session) => (session.id === result.id ? result : session)))
+      return result
     },
-    [data]
+    [agent.id, client, mutate]
   )
 
   return {