refactor: internalize nextFrame() into fixture/helper methods (#11166)

## Summary

Internalize `nextFrame()` calls into fixture/helper methods so spec
authors don't need to remember to call it after common operations.
`nextFrame()` waits for one `requestAnimationFrame` (~16ms) — an extra
call is always safe, making this a low-risk refactor.

## Changes

### Phase 1: `SettingsHelper.setSetting()`
`setSetting()` now calls `nextFrame()` internally. Removed 15 redundant
calls across 7 files.

### Phase 2: `CommandHelper.executeCommand()`
`executeCommand()` now calls `nextFrame()` internally. Removed 15
redundant calls across 7 files, including the now-redundant call in
`AppModeHelper.toggleAppMode()`.

### Phase 3: `WorkflowHelper.loadGraphData()`
New helper wraps `page.evaluate(loadGraphData)` + `nextFrame()`.
Migrated `SubgraphHelper.serializeAndReload()` and `groupNode.spec.ts`.

### Phase 4: `NodeReference` cleanup
Removed redundant `nextFrame()` from `copy()`, `convertToGroupNode()`,
`resizeNode()`, `dragTextEncodeNode2()`, and
`convertDefaultKSamplerToSubgraph()`. Removed 6 spec-level calls after
`node.click('title')`.

### Phase 5: `KeyboardHelper.press()` and `delete()`
New convenience methods that press a key and wait one frame. Converted
40 `canvas.press(key)` + `nextFrame()` pairs across 13 spec files.

### Phase 6: `ComfyPage.expectScreenshot()`
New helper combines `nextFrame()` + `toHaveScreenshot()`. Converted 45
pairs across 12 spec files.

## Total impact
- **~130 redundant `nextFrame()` calls eliminated** across ~35
spec/helper files
- **3 new helper methods** added (`loadGraphData`, `press`/`delete`,
`expectScreenshot`)
- **2 existing methods** enhanced (`setSetting`, `executeCommand`)

## What was NOT changed
- `performance.spec.ts` frame-counting loops (intentional)
- `ComfyMouse.ts` / `CanvasHelper.ts` (already internalized)
- `SubgraphHelper.packAllInteriorNodes()` (deliberate orchestration)
- Builder helpers (already internalized)

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-11166-refactor-internalize-nextFrame-into-fixture-helper-methods-33f6d73d3650817bb5f6fb46e396085e)
by [Unito](https://www.unito.io)

---------

Co-authored-by: Amp <amp@ampcode.com>

browser_tests/fixtures/helpers/SubgraphHelper.ts

@@ -465,11 +465,7 @@ export class SubgraphHelper {
     const serialized = await this.page.evaluate(() =>
       window.app!.graph!.serialize()
     )
-    await this.page.evaluate(
-      (workflow: ComfyWorkflowJSON) => window.app!.loadGraphData(workflow),
-      serialized as ComfyWorkflowJSON
-    )
-    await this.comfyPage.nextFrame()
+    await this.comfyPage.workflow.loadGraphData(serialized as ComfyWorkflowJSON)
   }
 
   async convertDefaultKSamplerToSubgraph(): Promise<NodeReference> {
@@ -477,14 +473,12 @@ export class SubgraphHelper {
     const ksampler = await this.comfyPage.nodeOps.getNodeRefById('3')
     await ksampler.click('title')
     const subgraphNode = await ksampler.convertToSubgraph()
-    await this.comfyPage.nextFrame()
     return subgraphNode
   }
 
   async packAllInteriorNodes(hostNodeId: string): Promise<void> {
     await this.comfyPage.vueNodes.enterSubgraph(hostNodeId)
     await this.comfyPage.settings.setSetting('Comfy.VueNodes.Enabled', false)
-    await this.comfyPage.nextFrame()
     await this.comfyPage.canvas.dispatchEvent('pointerdown', {
       bubbles: true,
       cancelable: true,