REM parity: CreateTopic

[giu-Expedibox]

User story

As a REM operator, I want to create a legacy topic from the app, so that compatible clients can use a new shared channel without a separate console.

Acceptance criteria

• A user can create a legacy topic from REM and see the saved result in the app.
• REM sends the exact southbound command 'CreateTopic' and surfaces accepted, result, and rejected outcomes in the UI.
• Returned data or state changes flow through the native runtime/projection path and refresh the relevant REM screen after completion.
• The closest automated tests and operator-facing docs are updated.

Implementation notes

• Add guarded admin workflows on top of a dedicated legacy/admin command client rather than scattering privileged command handling across views.
• Keep destructive actions explicit with confirmation, clear rejection handling, and operator-facing diagnostics in the UI.
• Keep transport, persistence, and response handling in Rust/native projections; keep Vue stores focused on command dispatch and projection refresh.