fix(relay): propagate authenticated scope

[wolfy-j]

Summary

• propagate websocket metadata scope_id into relay user hub identity
• preserve user_metadata when recreating the relay actor
• add focused relay central identity tests for authenticated scope propagation and legacy fallback

Validation

• cd src/relay/src && wippy lint --json -> 0 errors, 0 warnings
• cd src/relay/src && wippy run -o wippy.relay:central.service:host=wippy.terminal:host -o wippy.relay.env:user_security_scope:default=app.security:user -o wippy.relay.env:host:default=wippy.terminal:host test central -> 2/2 passed

Note

The broader relay test command still exposes an unrelated pre-existing user_test environment/policy issue, so this PR stays scoped to central relay identity propagation.