lint: add tsconfig for browser_tests, fix existing violations (#5633)

## Summary

See https://typescript-eslint.io/blog/project-service/ for context.
Creates a browser_tests specific tsconfig so that they can be linted.

Does not add a package.json script to do the linting yet, but `pnpm exec
eslint browser_tests` should work for now.

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-5633-lint-add-tsconfig-for-browser_tests-fix-existing-violations-2726d73d3650819d8ef2c4b0abc31e14)
by [Unito](https://www.unito.io)

tests-ui/tests/store/workflowStore.test.ts

@@ -3,9 +3,11 @@ import { beforeEach, describe, expect, it, vi } from 'vitest'
 import { nextTick } from 'vue'
 
 import type { Subgraph } from '@/lib/litegraph/src/litegraph'
-import {
+import type {
   ComfyWorkflow,
-  LoadedComfyWorkflow,
+  LoadedComfyWorkflow
+} from '@/platform/workflow/management/stores/workflowStore'
+import {
   useWorkflowBookmarkStore,
   useWorkflowStore
 } from '@/platform/workflow/management/stores/workflowStore'