feat: add live preview method setting for prompt execution (#7385)

## Summary

Add frontend setting to override live preview method per prompt
execution.

## Changes

- **What**: New setting `Comfy.Execution.PreviewMethod` allows users to
override preview method (default/none/auto/latent2rgb/taesd) from
frontend. Applied to Queue Prompt, Queue Front, Run Selected Nodes, and
Auto Queue.
- **Dependencies**: Requires backend support from
comfyanonymous/ComfyUI#11261

## Review Focus

- `'default'` option does not send `preview_method` to backend (uses
server CLI setting)
- Legacy UI intentionally not modified (deprecated, maintains backward
compatibility)
- `versionAdded: '1.35.3'` assigned tentatively; adjust as needed for
actual release version

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-7385-feat-add-live-preview-method-setting-for-prompt-execution-2c66d73d365081759c9cebaec29f451c)
by [Unito](https://www.unito.io)

src/scripts/app.ts

@@ -1344,6 +1344,9 @@ export class ComfyApp {
     try {
       while (this.queueItems.length) {
         const { number, batchCount, queueNodeIds } = this.queueItems.pop()!
+        const previewMethod = useSettingStore().get(
+          'Comfy.Execution.PreviewMethod'
+        )
 
         for (let i = 0; i < batchCount; i++) {
           // Allow widgets to run callbacks before a prompt has been queued
@@ -1358,7 +1361,8 @@ export class ComfyApp {
             api.authToken = comfyOrgAuthToken
             api.apiKey = comfyOrgApiKey ?? undefined
             const res = await api.queuePrompt(number, p, {
-              partialExecutionTargets: queueNodeIds
+              partialExecutionTargets: queueNodeIds,
+              previewMethod
             })
             delete api.authToken
             delete api.apiKey