fix(ai-agent-node) - agent node execution error (#20534)

**Root cause:** getWorkflowRunContext(stepInfos) builds a Record<string,
unknown> from the previous steps' results. There is no workspaceId key
in it, so context.workspaceId as string silently evaluated to undefined.
That undefined was then passed all the way down to
WorkspaceCacheService.getOrRecompute, **which correctly throws** when
workspaceId is not a valid UUID.

Before : 
<img width="525" height="130" alt="Screenshot 2026-05-13 at 14 58 54"
src="https://github.com/user-attachments/assets/0549b4dc-7063-44e5-95a1-00a460a6d7f1"
/>

Introduced with billing v2 yesterday, since then, workspaceId is needed
to bill credit usage

packages/twenty-server/src/modules/workflow/workflow-executor/workflow-actions/ai-agent/ai-agent.workflow-action.ts

@@ -48,7 +48,7 @@ export class AiAgentWorkflowAction implements WorkflowAction {
     }
 
     const { agentId, prompt } = step.settings.input;
-    const workspaceId = context.workspaceId as string;
+    const workspaceId = runInfo.workspaceId;
 
     let agent: AgentEntity | null = null;