Add authorized file-root sync

AGENTS.md

@@ -138,9 +138,12 @@ Roadmap items should be actionable and checkable:
 - The CAS crate can build deterministic tree objects for local file trees and
   store those manifests as CAS blobs. The daemon can register and scan local
   file roots, reporting create/update/delete/rename changes without writing back
-  to the working tree. Durable local file-conflict records can be listed and
-  resolved manually; automatic cross-node conflict detection and file sync are
-  still roadmap work.
+  to the working tree. `geth cas root sync <node-id> <name>` can pull authorized
+  remote tree metadata and CAS tree bytes, recording a peer-qualified remote
+  root with path `remote:<node>:<name>` without applying files or overwriting
+  same-named local roots. Durable local file-conflict records can be listed and
+  resolved manually; automatic cross-node conflict detection and file application
+  are still roadmap work.
 - DB resources can be registered locally and report local-only status plus a
   read-only SQLite schema summary/hash and `crsql_changes` metadata when
   present. The DB crate and daemon can extract typed read-only `crsql_changes`