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/SHARING.md

@@ -47,6 +47,7 @@ a viewer are read-only.
 
 - **Invitations** wait in a banner at the top of the page until you accept or reject them. From a
   terminal: `pdfs invitations list`, then `accept ID` or `reject ID`.
-- **Saved public links** have their own view. `pdfs bookmarks` manages them.
+- **Saved public links** have their own view, listed by the name of what they point at.
+  `pdfs bookmarks` manages them.
 - **Leave…** a share you no longer need, or run `pdfs leave UID` with the ID from
   `pdfs shared-with-me`.