feat(cli,fuse,core): copy files and folders on Proton Drive

`pdfs copy PATH... NEW_PARENT` sends a new control request, Copy, which
copies a file with its content or a folder with its subtree on Proton
Drive through proton-drive-rs's copy_node. Nothing is downloaded or
uploaded. A name already taken in the destination gets the next free
" (n)" suffix through get_available_name.

A copy cannot wait in the queue, because Drive copies what it holds.
So it is refused offline, and while the mount still owes Drive part of
the node: a local placeholder, a queued op, unsaved writes, or, for a
folder, any queued op at all. Local-first does not change this.

DriveApi gains copy_node and get_available_name, and the fake drive
copies subtrees, so a FUSE sim test covers the copy, the suffix, the
folder subtree and both refusals. The activity feed logs a new Copy
kind, translated in every catalog.

Needs the proton-drive-rs release that adds copy_node; until then, build
with a [patch.crates-io] pointing at proton-sdk-rs.

docs/CHANGELOG.md

@@ -19,6 +19,10 @@ scratch (user data in `staging/` and `recovery/` is never touched by this).
   the app asks GitHub once a day and shows a banner with a **Download** button when a newer
   version is out. It is off by default, and not offered for packages that a package manager
   updates (COPR, the AUR, Nix) (#42).
+- **`pdfs copy` copies files and folders on Proton Drive**, without downloading or uploading
+  them: `pdfs copy ~/ProtonDrive/report.pdf ~/ProtonDrive/Archive`. A folder is copied with
+  everything in it, and a name already taken gets a " (1)" suffix. A file or folder with changes
+  that have not synced yet is refused until they have.
 
 ### Changed
 - **Reorganised documentation, now also on the