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/schemas/apiSchema.ts

@@ -372,6 +372,15 @@ const zNodeBadgeMode = z.enum(
   Object.values(NodeBadgeMode) as [string, ...string[]]
 )
 
+const zPreviewMethod = z.enum([
+  'default',
+  'none',
+  'auto',
+  'latent2rgb',
+  'taesd'
+])
+export type PreviewMethod = z.infer<typeof zPreviewMethod>
+
 const zSettings = z.object({
   'Comfy.ColorPalette': z.string(),
   'Comfy.CustomColorPalettes': colorPalettesSchema,
@@ -433,6 +442,7 @@ const zSettings = z.object({
   'Comfy.TreeExplorer.ItemPadding': z.number(),
   'Comfy.Validation.Workflows': z.boolean(),
   'Comfy.Workflow.SortNodeIdOnSave': z.boolean(),
+  'Comfy.Execution.PreviewMethod': zPreviewMethod,
   'Comfy.Workflow.WorkflowTabsPosition': z.enum(['Sidebar', 'Topbar']),
   'Comfy.Node.DoubleClickTitleToEdit': z.boolean(),
   'Comfy.WidgetControlMode': z.enum(['before', 'after']),