Integrate @embedpdf/plugin-thumbnail and build thumbnail sidebar with toggle

[cto-new]

Summary

Add support for the thumbnail plugin and provide a user-friendly thumbnail sidebar next to the PDF viewport. This enables quick page navigation via thumbnails and a toggle-able UI in the toolbar.

Details

• Install and pin @embedpdf/plugin-thumbnail to match @embedpdf/core version.
• Register the ThumbnailPluginPackage in the PDF container with a default width of 120.
• Implement a new ThumbnailSidebar component using ThumbnailsPane and ThumbImg to render per-page thumbnails with virtualization metadata.
• Wire the ThumbnailSidebar into the layout using the shadcn-ui Sidebar (right, floating) with a dedicated ThumbnailSidebar child.
• Add a ThumbnailSidebar to the PDF container layout (below the toolbar) so users see thumbnails alongside the main viewport.
• Extend the Toolbar to include a Toggle Thumbnails button (Images icon) that toggles the thumbnail sidebar.
• Update tsconfig to use @types/bun to fix type checks (pre-existing issue addressed as part of repo maintenance).
• Pin plugin-thumbnail version in package.json (no caret) to align with other embedded plugin versions.

Note

No breaking API changes; UI behavior updated to expose and control a thumbnail sidebar for easier page navigation.