Migrate off the OCA.Viewer global before Nextcloud 36

integration_excalidraw loads its viewer script from a listener on the viewer's load event:

• lib/Listener/LoadViewerListener.php:28: use OCA\Viewer\Event\LoadViewer;
• lib/Listener/LoadViewerListener.php: Util::addScript(Application::APP_ID, Application::APP_ID . '-viewer')

[!WARNING]
This fails quietly. OCA\Viewer\Event\LoadViewer stops existing, so the listener never fires,
the script is never added, and the handler inside it never registers. No error, excalidraw
files simply stop opening in the viewer.

The listener can go entirely. Register the handler from a script loaded with
\OCP\Util::addInitScript() instead, which is what puts it in place before the Files list takes
its first snapshot of the available actions. Handlers are also custom elements now rather
than Vue components handed to the viewer: you define the element on window.customElements and
register its tagname. The
registration walkthrough
covers both halves.

Unrelated, but while you are in there: lib/Listener/LoadViewerListener.php:51 has a leftover
error_log('LoadViewerListener::handle()').

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 with lib/Listener/LoadViewerListener.php and the script containing the current viewer handler, then read the nextcloud-viewer registration walkthrough and migration guide. Port initialization and custom-element registration to @nextcloud/viewer, remove the obsolete listener and error_log call, and verify Excalidraw files open with Viewer 7 and Nextcloud 36.