feat: use cloud backend thumbnail resize for image previews (#9298)

## Summary

- In cloud mode, large generated images (4K, 8K+) cause browser freezing
when loaded at full resolution for preview display
- The cloud backend (ingest service) now supports a `res` query
parameter on `/api/view` that returns server-side resized JPEG (quality
80, max 512px) instead of redirecting to the full-size GCS original
- This PR adds `&res=512` to all image preview URLs in cloud mode,
reducing browser decode overhead from tens of MB to tens of KB
- Downloads still use the original resolution (no `res` param)
- No impact on localhost/desktop builds (`isCloud` compile-time
constant)

### without `?res`

302 -> png downloads
<img width="808" height="564" alt="스크린샷 2026-02-28 오후 6 53 03"
src="https://github.com/user-attachments/assets/7c1c62dd-0bc4-468d-9c74-7b98e892e126"
/>
<img width="323" height="137" alt="스크린샷 2026-02-28 오후 6 52 52"
src="https://github.com/user-attachments/assets/926aa0c4-856c-4057-96a0-d8fbd846762b"
/>

200 -> jpeg

### with `?res`
<img width="811" height="407" alt="스크린샷 2026-02-28 오후 6 51 55"
src="https://github.com/user-attachments/assets/d58d46ae-6749-4888-8bad-75344c4d868b"
/>


### Changes

- **New utility**: `getCloudResParam(filename?)` returns `&res=512` in
cloud mode for image files, empty string otherwise
- **Core stores**: `imagePreviewStore` appends `res` to node output
URLs; `queueStore.ResultItemImpl` gets a `previewUrl` getter (separates
preview from download URLs)
- **Applied to**: asset browser thumbnails, widget dropdown previews,
linear mode indicators, image compare node, background image upload

### Intentionally excluded

- Downloads (`getAssetUrl`) — need original resolution
- Mask editor — needs pixel-accurate data
- Audio/video/3D files — `res` only applies to raster images
- Execution-in-progress previews — use WebSocket blob URLs, not
`/api/view`

## Test plan

- [x] Unit tests for `getCloudResParam()` (5 tests: cloud/non-cloud,
image/non-image, undefined filename)
- [x] `pnpm typecheck` passes
- [x] `pnpm lint` passes
- [x] All 5332 unit tests pass
- [x] Manual verification on cloud.comfy.org: `res=512` returns 200 with
resized JPEG; without `res` returns 302 redirect to GCS PNG original

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

src/renderer/extensions/linearMode/LinearControls.vue

@@ -10,6 +10,7 @@ import Button from '@/components/ui/button/Button.vue'
 import { extractVueNodeData } from '@/composables/graph/useGraphNodeManager'
 import type { LGraphNode } from '@/lib/litegraph/src/LGraphNode'
 import { useBillingContext } from '@/composables/billing/useBillingContext'
+import { appendCloudResParam } from '@/platform/distribution/cloudPreviewUtil'
 import SubscribeToRunButton from '@/platform/cloud/subscription/components/SubscribeToRun.vue'
 import { useSettingStore } from '@/platform/settings/settingStore'
 import { useTelemetry } from '@/platform/telemetry'
@@ -88,13 +89,16 @@ function getDropIndicator(node: LGraphNode) {
   const filename = node.widgets?.[0]?.value
   const resultItem = { type: 'input', filename: `${filename}` }
 
+  const buildImageUrl = () => {
+    if (!filename) return undefined
+    const params = new URLSearchParams(resultItem)
+    appendCloudResParam(params, String(filename))
+    return api.apiURL(`/view?${params}${app.getPreviewFormatParam()}`)
+  }
+
   return {
     iconClass: 'icon-[lucide--image]',
-    imageUrl: filename
-      ? api.apiURL(
-          `/view?${new URLSearchParams(resultItem)}${app.getPreviewFormatParam()}`
-        )
-      : undefined,
+    imageUrl: buildImageUrl(),
     label: t('linearMode.dragAndDropImage'),
     onClick: () => node.widgets?.[1]?.callback?.(undefined)
   }

src/renderer/extensions/vueNodes/widgets/components/WidgetSelectDropdown.vue

@@ -4,6 +4,7 @@ import { computed, provide, ref, toRef, watch } from 'vue'
 import { useI18n } from 'vue-i18n'
 
 import { useTransformCompatOverlayProps } from '@/composables/useTransformCompatOverlayProps'
+import { appendCloudResParam } from '@/platform/distribution/cloudPreviewUtil'
 import { SUPPORTED_EXTENSIONS_ACCEPT } from '@/extensions/core/load3d/constants'
 import { useAssetFilterOptions } from '@/platform/assets/composables/useAssetFilterOptions'
 import {
@@ -460,7 +461,9 @@ function getMediaUrl(
   type: 'input' | 'output' = 'input'
 ): string {
   if (!['image', 'video'].includes(props.assetKind ?? '')) return ''
-  return `/api/view?filename=${encodeURIComponent(filename)}&type=${type}`
+  const params = new URLSearchParams({ filename, type })
+  appendCloudResParam(params, filename)
+  return `/api/view?${params}`
 }
 </script>