feat: add KSampler live previews to assets sidebar jobs (#8723)

## Summary
Show live KSampler previews on active job cards/list items in the Assets
sidebar, while preserving existing fallback behavior.

## Changes
- **What**:
- Added a prompt-scoped job preview store (`jobPreviewStore`) gated by
`Comfy.Execution.PreviewMethod`.
- Wired `b_preview_with_metadata` handling to map previews by
`promptId`.
- Extended queue job view model with `livePreviewUrl` and consumed it in
both sidebar list and grid active job UIs.
  - Cleared prompt previews on execution reset.
- Added ref-counted shared blob URL lifecycle utility (`objectUrlUtil`)
and updated preview stores to retain/release shared URLs so each preview
event creates one object URL.
- Added/updated unit coverage in `useJobList.test.ts` for preview
enable/disable mapping.

## Review Focus
- Object URL lifecycle correctness across node previews and job previews
(retain/release behavior).
- Preview gating behavior when `Comfy.Execution.PreviewMethod` is
`none`.
- Active job UI fallback behavior (`livePreviewUrl` -> `iconImageUrl`).

## Screenshots (if applicable)
<img width="808" height="614" alt="image"
src="https://github.com/user-attachments/assets/37c66eb2-8c28-4eb4-bb86-5679cb77d740"
/>
<img width="775" height="345" alt="image"
src="https://github.com/user-attachments/assets/aa420642-b0d4-4ae6-b94a-e7934b5df9d6"
/>


┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-8723-feat-add-KSampler-live-previews-to-assets-sidebar-jobs-3006d73d365081aeb81dd8279bf99f94)
by [Unito](https://www.unito.io)

src/scripts/app.ts

@@ -61,6 +61,7 @@ import { useExecutionStore } from '@/stores/executionStore'
 import { useExtensionStore } from '@/stores/extensionStore'
 import { useFirebaseAuthStore } from '@/stores/firebaseAuthStore'
 import { useNodeOutputStore } from '@/stores/imagePreviewStore'
+import { useJobPreviewStore } from '@/stores/jobPreviewStore'
 import { KeyComboImpl } from '@/platform/keybindings/keyCombo'
 import { useKeybindingStore } from '@/platform/keybindings/keybindingStore'
 import { useModelStore } from '@/stores/modelStore'
@@ -86,6 +87,10 @@ import {
   fixLinkInputSlots,
   isImageNode
 } from '@/utils/litegraphUtil'
+import {
+  createSharedObjectUrl,
+  releaseSharedObjectUrl
+} from '@/utils/objectUrlUtil'
 import {
   findLegacyRerouteNodes,
   noNativeReroutes
@@ -701,12 +706,13 @@ export class ComfyApp {
 
     api.addEventListener('b_preview_with_metadata', ({ detail }) => {
       // Enhanced preview with explicit node context
-      const { blob, displayNodeId } = detail
+      const { blob, displayNodeId, promptId } = detail
       const { setNodePreviewsByExecutionId, revokePreviewsByExecutionId } =
         useNodeOutputStore()
+      const blobUrl = createSharedObjectUrl(blob)
+      useJobPreviewStore().setPreviewUrl(promptId, blobUrl)
       // Ensure clean up if `executing` event is missed.
       revokePreviewsByExecutionId(displayNodeId)
-      const blobUrl = URL.createObjectURL(blob)
       // Preview cleanup is handled in progress_state event to support multiple concurrent previews
       const nodeParents = displayNodeId.split(':')
       for (let i = 1; i <= nodeParents.length; i++) {
@@ -714,6 +720,7 @@ export class ComfyApp {
           blobUrl
         ])
       }
+      releaseSharedObjectUrl(blobUrl)
     })
 
     api.init()