Library persistence fails if user's Templates folder was deleted

[Mimovnik]

Whiteboard library persistence fails if the user's "Templates" folder has been deleted.

Environment

• Nextcloud deployment: Nextcloud AIO
• Whiteboard version: 1.5.9
• Browser: Brave / Chromium

Steps to reproduce

1. Remove the user's Templates/ folder from Nextcloud Files (or rename to TemplatesBackup)
2. Open any .whiteboard file.
3. Import a library. Library -> three dots -> Open -> select previously downloaded .excalidrawlib from a file picker
4. Confirm the imported library appears in the current session.
5. Reload the page and enter the .whiteboard file.
6. Imported library disapears.

Actual behavior

The imported library disappears after reload.

In browser DevTools, the library save request fails:

PUT /apps/whiteboard/library -> 404

Expected behavior

Whiteboard should persist the imported library, even if the user deleted the default Templates/ folder.

Possible solution

1. Ensure the user's Templates/ folder exists before reading/writing personal.excalidrawlib.
2. Recreate Templates/ folder when importing a library.

[Mimovnik]

I wonder if Whiteboard should avoid relying on the user-visible Templates/ folder for saving libraries.

From the Files UI, that folder looks optional, so users can delete it without realizing it breaks library persistence. That is what happened in my case: importing the library looked fine at first, but after reload it disappeared because saving failed.

For now, the simple fix is probably just to recreate Templates/ if it is missing before writing personal.excalidrawlib.
Moving Whiteboard library data somewhere app-owned (eg. .whiteboard-libraries/ could be a separate discussion.