feat: support Cursor as an agent runtime

[ddhjy]

Summary

Multica currently supports agent backends like Claude Code and Codex. It would be useful to also support Cursor as an available agent/runtime option.

Why this matters

• Some teams already standardize on Cursor for day-to-day AI-assisted development.
• Adding Cursor support would lower adoption friction for teams evaluating Multica.
• It would make the local agent runtime story more complete across the major coding-agent tools.

Proposed support

• Detect and register Cursor as an available runtime/provider.
• Allow assigning work to Cursor-backed agents the same way as existing providers.
• Document setup, authentication, and any runtime-specific limitations.

Expected outcome

Users should be able to connect Cursor and run Multica agent tasks through it without needing to switch to another coding agent tool.

[Bohan-J]

Noted

[songjiayang]

很多公司用的是cursor，可以考虑支持下，cursor agent cli 也不错

[sanjay3290]

For reference, I just went through the process of adding a new agent provider (Gemini CLI) in #755. The pattern is:

1. New server/pkg/agent/gemini.go implementing the Backend interface (~135 LOC)
2. Registration in server/internal/daemon/config.go (probe for binary on PATH)
3. Case in agent.New() factory
4. GEMINI.md injection in execenv/runtime_config.go

If someone wants to add Cursor CLI support, the Gemini PR is a good template to follow. The main question is what Cursor's non-interactive/headless invocation looks like (flags for prompt input, output format, auto-approve tools, etc.).

[lehno]

We have the cursor subscription and would be really good to have it here

[LAlvarez-Doma]

Ditto

[Bohan-J]

working on it ⌨️

[lcalvarez]

Looks like there's already a PR for it (haven't reviewed): #1057