feat: apply per-persona MCP server overrides in multi-persona panel

[andrewchumchal]

Summary

The Persona type already has a defaultMcpServerIds?: string[] field, but sendPersonaTurn in the multi-persona extension doesn't apply it. Currently all personas in a panel share the same enabledMcpServerIds from the conversation request.

Expected behaviour

When a persona has defaultMcpServerIds set, those server IDs should be merged with the conversation's enabled MCP servers for that persona's turn. Other personas in the same panel are unaffected.

Proposed change

In sendPersonaTurn (multi-persona index.tsx), when building personaRequest:

const personaRequest: ChatRequest = {
  ...request,
  messageId,
  providerId: persona.defaultProviderId ?? request.providerId,
  model: persona.defaultModel ?? request.model,
  parameters: { ...request.parameters, ...(persona.parameters ?? {}) },
  systemPrompt,
  enabledMcpServerIds: [
    ...new Set([...request.enabledMcpServerIds, ...(persona.defaultMcpServerIds ?? [])]),
  ],
};

Use case

A "SCF Expert" persona can have a Salesforce-specific MCP server (e.g. one that queries Salesforce schema or documentation) auto-enabled, while a "Team Expert" persona has a different set of tools, all within the same multi-persona conversation.