feat(historyV2): load workflows for images (#6384)

## Summary

Hooked up the "Load Workflow" action to our `history_v2` API.

Note: Our cloud envs were being stress tested right now so images are
loading at time of recording. Images were loading for me during
development before I had time to create the video.


## Screenshots 📷 



https://github.com/user-attachments/assets/02145504-ceae-497b-9049-553796d698da



┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-6384-Feat-history-v2-workflows-29b6d73d365081bcb706fe799b8ce66a)
by [Unito](https://www.unito.io)

src/platform/workflow/cloud/getWorkflowFromHistory.ts

@@ -0,0 +1,21 @@
+import type { ComfyWorkflowJSON } from '@/platform/workflow/validation/schemas/workflowSchema'
+import type { PromptId } from '@/schemas/apiSchema'
+
+export async function getWorkflowFromHistory(
+  fetchApi: (url: string) => Promise<Response>,
+  promptId: PromptId
+): Promise<ComfyWorkflowJSON | undefined> {
+  try {
+    const res = await fetchApi(`/history_v2/${promptId}`)
+    const json = await res.json()
+
+    const historyItem = json[promptId]
+    if (!historyItem) return undefined
+
+    const workflow = historyItem.prompt?.extra_data?.extra_pnginfo?.workflow
+    return workflow ?? undefined
+  } catch (error) {
+    console.error(`Failed to fetch workflow for prompt ${promptId}:`, error)
+    return undefined
+  }
+}

src/platform/workflow/cloud/index.ts

@@ -0,0 +1,10 @@
+/**
+ * Cloud: Fetches workflow by prompt_id. Desktop: Returns undefined (workflows already in history).
+ */
+import { isCloud } from '@/platform/distribution/types'
+
+import { getWorkflowFromHistory as cloudImpl } from './getWorkflowFromHistory'
+
+export const getWorkflowFromHistory = isCloud
+  ? cloudImpl
+  : async () => undefined