[Feature]: Agent Server exclusive mode support

[ulivz]

Which desktop app does this feature request relate to?

• Agent-TARS (cli, server, agent, tool etc.)

What problem does this feature solve?

Agent Server currently supports concurrent execution, but there's no way to configure exclusive mode for scenarios requiring single-agent execution without interference.

What does the proposed features look like?

Add server.exclusive option in AgentOptions to enable exclusive mode:

interface AgentOptions {
  server: {
    exclusive?: boolean; // default: false
    // other server options...
  }
}

When server.exclusive: true, the server should reject new requests while an agent is running.