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/CLI.md

@@ -58,6 +58,7 @@ browser, complete it, then press Enter.
 | `pdfs mkdir PARENT NAME` | Create a folder. |
 | `pdfs rename PATH NEW_NAME` | Rename a file or folder. |
 | `pdfs move PATH... NEW_PARENT` | Move one or more files or folders into another folder. The two may be in different locations (My files, an on-demand or a mirrored synced folder); the move happens on Proton Drive, without downloading or uploading anything. |
+| `pdfs copy PATH... NEW_PARENT` | Copy one or more files or folders into another folder in My files. The copy happens on Proton Drive, without downloading or uploading anything; a name already taken gets a " (1)" suffix. Changes that have not synced yet must sync first. |
 | `pdfs rm PATH` | Move to the Trash. |
 | `pdfs upload SOURCES... [-t FOLDER]` | Upload local files and folders (recursively) in the background. Follow with `pdfs transfers`. |
 | `pdfs refresh [TARGET] [--full]` | Forget a cached listing so the next read fetches it again. `TARGET` is a folder, `trash` or `photos`; `--full` with `photos` re-reads every photo's metadata. |