Make sorting emails into folders feeling more performant

Is your feature request related to a problem? Please describe.

If you have a lot of folders and you want to sort your mails from the inbox into them, it always takes quite some time to find the right folder. This feels way slower than in other solutions like Thunderbird, although the technical performance might be the same.

Describe the solution you'd like

Multiple things could be improved:

• when grabbing an email with drag & drop, don't change the folder tree. Right now all folders are opened. This however leads to quite some scrolling if you have many folders. In TB, you can just open the folders you need right now and it stays like this.
• allow mouse wheel scrolling while drag & drop operations on the folder tree
• allow to move multiple mails via three dot menu. Currently you don't get this option when selecting multiple emails.

Describe alternatives you've considered

Don't use Nextcloud mail for this, but in the app there isn't a good alternative.

Additional context

No response

Start by tracing the folder-tree drag-and-drop entry point and the three-dot menu for multi-selected emails. Reproduce sorting with many folders, checking whether the tree expands and whether the folder tree scrolls during dragging. Done means preserving the tree state, supporting mouse-wheel scrolling during drag-and-drop, and exposing move actions for multiple selected emails.