feat(webuiapps): add minimal MCP stdio bridge for external agent integration

[CrepuscularIRIS]

Summary

This PR adds a minimal MCP stdio bridge in the Vite dev backend so OpenRoom can talk to external MCP servers (for multi-agent integration use cases).

What Changed

• Added MCP server config persistence at ~/.openroom/mcp-servers.json
• Added backend endpoints in apps/webuiapps/vite.config.ts:
  • GET/POST /api/mcp-servers
  • GET /api/mcp-tools
  • POST /api/mcp-call
• Implemented stdio JSON-RPC framing (Content-Length) and request timeout handling
• Added MCP helper utilities:
  • apps/webuiapps/src/lib/mcpBridgeTools.ts
• Added unit tests:
  • apps/webuiapps/src/lib/__tests__/mcpBridgeTools.test.ts

Why

OpenRoom currently has a strong chat/tool UX. This bridge lets OpenRoom act as a frontend hub while delegating reasoning/tools to external MCP-compatible agents/services.

Validation

• pnpm --dir apps/webuiapps test -- --run (113 tests passed)
• pnpm --dir apps/webuiapps build (success)
• Local smoke test with a temporary stdio MCP server:
  • POST /api/mcp-servers -> saved server config
  • GET /api/mcp-tools -> discovered echo tool
  • POST /api/mcp-call -> successful tool call response

Notes

• This is intentionally minimal backend plumbing first.
• UI-level MCP management and routing policies can be iterated in follow-up PRs.