[Feature] Add a Download All button

**Packages**

Media

**Describe the solution you'd like**

On the Control Panel when viewing a publication you have to download each video individually. Instead we could add a Download button.

- Only shows if there are 1+ videos not downloaded
- Will download all items
- Sends a request through IPC
- Sets the downloading state of each tile
- Sets all videos to downloaded when complete

**Describe alternatives you've considered**

We can still download them individually, it's just slow

**Additional context**

N/A

Start at the Control Panel publication view and trace the existing individual video download flow, including its IPC request and tile downloading state. Implement the described bulk-download behavior and verify that the button appears only when videos remain and that all videos become downloaded when the operation completes.

Written by the indexing model from the issue text.