feat(gui): make a copy and copy to another folder in My files

The entry menu gains Make a Copy, which copies an item next to itself, and
Copy To…, which reuses the move folder picker limited to My files; Copy
To… is also in the selection menu. Both send Request::Copy, so the copy is
made on Proton Drive.

The move and copy reports share one request loop. Docs describe the new
actions, and the changelog notes that saved public links now show their
names once the SDK decrypts them.

docs/FILES.md

@@ -61,6 +61,12 @@ a list view, sorting, thumbnails (including camera RAW previews), multi-select,
 to upload. **Details** (Alt+Enter) shows the size, dates, sharing and version history of the
 selected item.
 
+Right-click an item for more. **Make a Copy** copies it into the same folder, and **Copy To…**
+copies it, or a whole selection, into another folder in My files. The copy is made on Proton
+Drive, so nothing is downloaded or uploaded, and a name already taken gets a " (1)" suffix. An
+item with changes that have not reached Proton Drive yet can be copied once they have. From a
+terminal: `pdfs copy PATH... NEW_PARENT`.
+
 ## Trash
 
 Deleted files go to the Trash, both from `~/ProtonDrive` and from the app. The **Trash** page