[Remote rendering 5.2] Replace local render window with pvserver connection

### 📝 Description of the feature

Implement ParaView's pvserver client connection so RemoteRenderer renders against pvserver instead of the local render-window stand-in used by the initial spike, then remove that stand-in.

Re-verify the Phase 4 behaviour (streaming, per-part state, camera interaction, coalescing, connect/reconnect, live refresh) against the real ParaView server backend.

### Acceptance Criteria

Remote rendering behaviour holds with pvserver as the backend.

### 💵 Business Value

_No response_

### 🔗 Useful links and references

_No response_

Start by locating RemoteRenderer and the local render-window stand-in from the initial spike. Review how the Phase 4 behaviours are currently verified, then connect rendering to pvserver and remove the stand-in. Done means streaming, per-part state, camera interaction, coalescing, connect/reconnect, and live refresh work against the real ParaView server backend.

Written by the indexing model from the issue text.