feat: Jan Tool Use - MCP frontend implementation

[louis-menlo]

Implement Jan Tool Use UI

Summary

This PR introduces tool usage in Jan's frontend, allowing chat/completions requests to include tools. The assistant can now output tool call instructions and follow up with appropriate requests.

Changes

• Include tools in chat/completions requests
• Group tool use messages with assistant messages
• Available tools information
• Add a shortcut to quickly access the MCP servers config file

Next Steps

• Improve UI/UX for tool use messages
• Implement shortcut navigation for MCP server configuration

Testing

1. Start Jan and open the chat interface.
2. Trigger a request that requires tool usage (e.g., a query that invokes a specific tool).
3. Verify that the tool call is executed correctly and follow-up requests are made.

Notes

• The UI for tool use grouping is still a work in progress.
• Navigation shortcut implementation is pending.

Thoughts

• Should we deprecate chat/completions entities and use the OpenAI client SDK directly / or Vercel AI SDK?

Screenshots

mcp_config.json

Issues

#4824

[louis-menlo]

This PR is getting big - Merge back to the root PR, upcoming updates on new PRs