[Bug]: MultiVMWorkload roles are hardcoded in orchestrator

[mrhillsman]

Bug Description

`cmd/virtwork/main.go` (lines 254-256) hardcodes `roles := []string{"server", "client"}` when iterating over a `MultiVMWorkload`. The `MultiVMWorkload` interface defines `UserdataForRole(role string, ...)` but provides no method for a workload to declare its supported roles. If a future MultiVMWorkload implementation uses different role names, the orchestrator will silently pass the wrong roles.

Steps to Reproduce

1. Implement a new `MultiVMWorkload` with roles other than "server" and "client" (e.g., "primary" and "replica")
2. Register the workload and run it via `virtwork run`
3. The orchestrator passes "server" and "client" roles regardless of the workload's actual role names

Expected Behavior

`MultiVMWorkload` interface should expose a `Roles() []string` method, and the orchestrator should call it instead of hardcoding role names.

Actual Behavior

Roles are hardcoded as `["server", "client"]` in the orchestrator, silently breaking any multi-VM workload that uses different role names.

Command

virtwork run

Workload Type

network

Go Version

Not provided

Deployment Mode

Not provided

Additional Context

Severity: Medium

Files:

• `cmd/virtwork/main.go:254-256` — hardcoded roles
• `internal/workloads/workload.go:57-60` — `MultiVMWorkload` interface (missing `Roles() []string` or equivalent)