fix: clean up unused icons and add LoadImage lucide icon override (#9359)

## Summary

Remove 46 unused snake_case SVG icons from design-system and use lucide
icon for LoadImage.

## Changes

- **What**: Remove unreferenced snake_case SVG files, replace LoadImage
custom icon with `lucide--image-up`, add `preview-image.svg` (renamed
from `image-preview.svg` to match `kebabCase('PreviewImage')`), extract
`ESSENTIALS_ICON_OVERRIDES` to `essentialsNodes.ts`
- Remove `load-image` from safelist in `style.css`

<img width="307" height="701" alt="image"
src="https://github.com/user-attachments/assets/de5e1bde-03eb-415e-ac76-f2e653a5eeb2"
/>

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-9359-fix-clean-up-unused-icons-and-add-LoadImage-lucide-icon-override-3186d73d36508159be05ce6f4145be56)
by [Unito](https://www.unito.io)

src/constants/essentialsNodes.ts

@@ -6,6 +6,17 @@
  * Source: https://www.notion.so/comfy-org/2fe6d73d365080d0a951d14cdf540778
  */
 
+export const ESSENTIALS_ICON_OVERRIDES: Record<string, string> = {
+  LoadImage: 'icon-s1.3-[lucide--image-up]',
+  LoadImageOutput: 'icon-s1.3-[lucide--image-up]',
+  SaveImage: 'icon-s1.3-[lucide--image-down]',
+  PrimitiveStringMultiline: 'icon-s1.3-[lucide--text]',
+  ImageCrop: 'icon-s1.3-[lucide--crop]',
+  VideoCrop: 'icon-s1.3-[lucide--crop]',
+  KlingLipSyncAudioToVideoNode: 'icon-s1.3-[lucide--mic-vocal]',
+  WebcamCapture: 'icon-s1.3-[lucide--camera]'
+}
+
 export const ESSENTIALS_CATEGORIES = [
   'basics',
   'text generation',