bug: when no clients in workspace.yaml, allagents should default to universal client (add it automatically)

[christso]

Why

currently if no clients added, no artifacts are created. Tis is counter intuitive.

Proposal

if no clients in workspace.yaml, and you run allagents plugin install or workspace sync, it should show a warning that no clients were added, so no artifacts created.

Perform e2e testing yourself to confirm what message you see. Also ensure that that the message aligns with the actual file operations.