Add Volt Agent

Add AG-UI support to [VoltAgent](https://voltagent.dev).

## What is VoltAgent?

VoltAgent is an open source TypeScript AI agent framework for building production-grade multi-agent systems. It ships with memory, tool use, multi-step workflows, and provider-agnostic LLM support out of the box, paired with VoltOps — a cloud console for observability, evals, and deployment.

- Site: https://voltagent.dev
- Repo: https://github.com/voltagent/voltagent

## Getting started with the integration

The AG-UI repo has a step-by-step guide for adding new framework integrations:

- **Contributing guide:** [CONTRIBUTING.md](https://github.com/ag-ui-protocol/ag-ui/blob/main/CONTRIBUTING.md)
- **Integration walkthrough:** [Step-by-Step Guide to Adding an Integration PR](https://github.com/ag-ui-protocol/ag-ui/blob/main/CONTRIBUTING.md#step-by-step-guide-to-adding-an-integration-pr)
- **Reference implementations:** [`integrations/langgraph/`](https://github.com/ag-ui-protocol/ag-ui/tree/main/integrations/langgraph), [`integrations/mastra/`](https://github.com/ag-ui-protocol/ag-ui/tree/main/integrations/mastra), [`integrations/adk-middleware/`](https://github.com/ag-ui-protocol/ag-ui/tree/main/integrations/adk-middleware)
- **CODEOWNERS:** [.github/CODEOWNERS](https://github.com/ag-ui-protocol/ag-ui/blob/main/.github/CODEOWNERS)

High-level steps from the guide:
1. Add an integration folder under `integrations/voltagent/` with a `typescript/` package and `examples/`
2. Register the integration in the Dojo (`apps/dojo/src/agents.ts`, `menu.ts`, `env.ts`)
3. Add Dojo prep + run scripts under `apps/dojo/scripts/`
4. Add e2e tests under `apps/dojo/e2e/tests/voltagentTests/`
5. Wire up CI in the test matrix
6. Community contributors become `CODEOWNERS` for the new integration and agree to maintain it for the community.