refactor: extract assetPath as standalone pure function (#10651)

## Summary

Extract `assetPath` from a `ComfyPage` method to a standalone pure
function, removing unnecessary coupling to the page object.

## Changes

- **What**: Moved `assetPath` to
`browser_tests/fixtures/utils/paths.ts`. `DragDropHelper` and
`WorkflowHelper` import it directly instead of receiving it via
`ComfyPage`. `ComfyPage.assetPath` kept as thin delegate for backward
compat.

## Review Focus

Structural-only refactor — no behavioral changes. The function was
already pure (no `this`/`page` usage).

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-10651-refactor-extract-assetPath-as-standalone-pure-function-3316d73d365081c0b0e0ce6dde57ef8e)
by [Unito](https://www.unito.io)

browser_tests/fixtures/helpers/WorkflowHelper.ts

@@ -7,6 +7,7 @@ import type {
 } from '../../../src/platform/workflow/validation/schemas/workflowSchema'
 import type { WorkspaceStore } from '../../types/globals'
 import type { ComfyPage } from '../ComfyPage'
+import { assetPath } from '../utils/paths'
 
 type FolderStructure = {
   [key: string]: FolderStructure | string
@@ -20,7 +21,7 @@ export class WorkflowHelper {
 
     for (const [key, value] of Object.entries(structure)) {
       if (typeof value === 'string') {
-        const filePath = this.comfyPage.assetPath(value)
+        const filePath = assetPath(value)
         result[key] = readFileSync(filePath, 'utf-8')
       } else {
         result[key] = this.convertLeafToContent(value)
@@ -59,7 +60,7 @@ export class WorkflowHelper {
 
   async loadWorkflow(workflowName: string) {
     await this.comfyPage.workflowUploadInput.setInputFiles(
-      this.comfyPage.assetPath(`${workflowName}.json`)
+      assetPath(`${workflowName}.json`)
     )
     await this.comfyPage.nextFrame()
   }