Migrate off the OCA.Viewer global before Nextcloud 36

Bookmarks opens an archived file in the viewer:

• src/components/SidebarBookmark.vue:366: OCA.Viewer.open({ ... })

There is no path based entry point any more: the viewer takes @nextcloud/files nodes. Either
build the node for the archived file, or hand openFolder(folder, file) a folder and let it
fetch.

OCA.Viewer is gone in Viewer 7.0.0. The viewer ships as the
@nextcloud/viewer library rather than a
bundled app, and nextcloud/server#63954 removes the viewer app from Nextcloud 36 altogether.

Roughly what it looks like:

import { canView, getViewer } from '@nextcloud/viewer'

// OCA.Viewer.open({ path }) / ({ fileInfo, list })
getViewer().open(nodes, file)          // @nextcloud/files nodes
getViewer().openFolder(folder, file)   // when a path is all you have, let it fetch

// OCA.Viewer.mimetypes.includes(mime) / availableHandlers
canView(node)

The part that is not a rename is that the viewer takes @nextcloud/files nodes now, not
fileinfo objects or path strings. Importing the package is also all it takes to get the viewer
onto the page: no LoadViewer event to dispatch, and nothing to check about whether the app is
enabled.

[!IMPORTANT]
There is no compatibility shim, which was a deliberate call, so this is a real port rather
than a rename. Nothing breaks until the server PR lands; after that these calls throw on
Nextcloud 36.

[!TIP]
The developer manual covers the migration under
Critical changes
(being added in nextcloud/documentation#15597), and the
README
has the full before/after table. Happy to help with the port, just ping me.

_{👾 This issue was written with the help of Claude Code.}

Start at src/components/SidebarBookmark.vue:366 and read the nextcloud-viewer README migration table, focusing on the node and folder entry points for archived files. Port this call away from OCA.Viewer and verify that the archived file opens without LoadViewer or an enabled viewer app on Nextcloud 36.