fix(host-agent): SECURITY — file manager copy/list no longer follow symlinks out of the jail

Automated security review (HIGH) caught a jail-escape my own review
missed: copy_recursive used fs::metadata (follows symlinks). A symlink
inside the jail pointing to e.g. /etc, then a 'copy' of its parent dir,
would dereference it and pull external content INTO the jail where it
could be read — a read-escape exfiltration. jail() validates only the
top-level src/dest; the recursive walk reintroduced the escape.

Fix: copy_recursive uses symlink_metadata and refuses any symlink
('symlinks are not followed across the jail boundary'). list() likewise
switched to symlink_metadata so it reports the link, never the
dereferenced target's size/type (info leak). Two regression tests added:
copy-symlink-exfil (asserts no external content lands inside) and
list-no-deref. 44/44 tests green. Rolled forward to alpha.4 (vulnerable
alpha.3 superseded).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

corrosion-host-agent/Cargo.lock

@@ -264,7 +264,7 @@ checksum = "773648b94d0e5d620f64f280777445740e61fe701025087ec8b57f45c791888b"
 
 [[package]]
 name = "corrosion-host-agent"
-version = "2.0.0-alpha.3"
+version = "2.0.0-alpha.4"
 dependencies = [
  "anyhow",
  "async-nats",