* Respect filerGroup in admin discovery
Admin discovery previously queried master cluster nodes with an empty filer group, so filers registered under a non-default group could not appear in the admin UI. Add an admin filerGroup flag and carry it through cluster-node discovery requests while preserving the empty default behavior.
Constraint: SeaweedFS master ListClusterNodes filters by exact filer_group.
Rejected: Discover all groups implicitly | no existing admin or shell behavior exposes cross-group discovery.
Confidence: high
Scope-risk: narrow
Directive: Keep admin cluster discovery scoped to the configured filerGroup unless an explicit all-groups API is added.
Tested: docker run --rm -v "$PWD:/src" -w /src golang:1.25 go test ./weed/admin/dash -run TestListClusterNodesRequest -count=1
Tested: docker run --rm -v "$PWD:/src" -w /src golang:1.25 go test ./weed/command -run '^$' -count=1
Not-tested: full repository test suite
* mini: pass filer group to admin cluster discovery
miniAdminOptions.filerGroup was never initialized, so startAdminServer
dereferenced a nil *string. Share the filer.filerGroup flag pointer so the
co-located admin queries the same group the filer registers under.
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Co-authored-by: Chris Lu <chris.lu@gmail.com>
