[Feature]: Batch move activities

[cqnykamp]

Before submitting

• I searched existing issues and did not find a duplicate request.

Affected area

Folder view

Layer

API (apps/api), Frontend (apps/app)

Problem

As brought up in this thread, moving items from one folder to another is a huge pain if there are a lot of items.

Proposed solution

Implement batch moving of items. We already have the ability to select multiple items, and some actions work on more than 1, so this is a natural feature.

Alternatives considered

No response

Additional context

The one complication to look out for when implementing this are the restrictions on what types of content can live inside what kinds of parents. The feature would need to decide what to do when some but not all of the moves are valid. Two options:

1. Reject and don't do anything
2. Execute all valid moves and ignore the rest