The filer is the authority on who is subscribed to its metadata stream
(FUSE/VFS mounts, S3, peer filers, ...), but its in-memory listener
registry only tracked clientId->epoch and was not exposed.
- Enrich the filer subscriber registry with name/type/address/path/
connected-time, populated in addClient and cleared in deleteClient so
it reflects currently-connected clients only.
- Add a ListMetadataSubscribers filer gRPC (optional client-type filter).
- Admin server fans out to every filer, filters to mount types
("mount" Go weed mount, "sw-vfs" Rust VFS), and renders a new
Cluster > Mount Clients page plus a Mount Clients dashboard section.
Read-only; no behavior change to the subscribe hot path.
Chris Lu
b883fedc23