feat: add grid view mode for multi-image batches in ImagePreview (#9241)

## Summary

Add grid view mode for multi-image batches in ImagePreview (Nodes 2.0),
replicating the Nodes 1.0 grid UX where all output images are visible as
clickable thumbnails.

## Changes

- **What**: Multi-image batches now default to a grid view showing all
thumbnails. Clicking a thumbnail switches to gallery mode for that
image. A persistent back-to-grid button sits next to navigation dots,
and hover action bars provide gallery toggle, download, and remove.
Replaced PrimeVue `Skeleton` with shadcn `Skeleton`. Added `viewGrid`,
`viewGallery`, `imageCount`, `galleryThumbnail` i18n keys.

## Review Focus

- Grid column count strategy: fixed breakpoints (2 cols ≤4, 3 cols ≤9, 4
cols 10+) vs CSS auto-fill
- Default view mode: grid for multi-image, gallery for single — matches
Nodes 1.0 behavior
- `object-contain` on thumbnails to avoid cropping (with `aspect-square`
containers for uniform cells)

Fixes #9162

<!-- Pipeline-Ticket: f8f8effa-adff-4ede-b1d3-3c4f04b9c4a0 -->

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-9241-feat-add-grid-view-mode-for-multi-image-batches-in-ImagePreview-3136d73d36508166895ed6c635150434)
by [Unito](https://www.unito.io)

---------

Co-authored-by: Alexander Brown <drjkl@comfy.org>
Co-authored-by: Alexander Brown <448862+DrJKL@users.noreply.github.com>
Co-authored-by: Amp <amp@ampcode.com>

src/locales/en/main.json

@@ -34,6 +34,8 @@
     "imageLightbox": "Image preview",
     "imagePreview": "Image preview - Use arrow keys to navigate between images",
     "videoPreview": "Video preview - Use arrow keys to navigate between videos",
+    "viewGrid": "Grid view",
+    "imageGallery": "image gallery",
     "galleryImage": "Gallery image",
     "galleryThumbnail": "Gallery thumbnail",
     "previousImage": "Previous image",