v3.1.1

fix: launch cursor agent from helix chef (#981)

chef already installs the helix docs mcp for cursor, but detect_agent
only looks for claude, codex, and opencode. if only `agent` is on path,
chef says no supported coding-agent cli and never launches.

repro:
1. agent on path, no claude/codex/opencode
2. helix chef
3. No supported coding-agent CLI was found in PATH (claude, codex,
opencode)

same captured launch path as codex/opencode.

tested with the existing cli fixture.

<!-- greptile_comment -->

<h3>Greptile Summary</h3>

This PR adds Cursor Agent detection and launch support to `helix chef`,
including permission-mode arguments and integration coverage.

- Adds `agent` as the lowest-priority supported coding-agent executable.
- Routes Cursor through the captured-output launch path.
- Adds unit and end-to-end coverage for Cursor argument construction and
selection.
- Leaves the README's supported-agent list out of date.

<details><summary><h3>Important Files Changed</h3></summary>

| Filename | Overview |
|----------|----------|
| crates/cli/src/commands/chef.rs | Adds Cursor detection, argv
construction, captured launch routing, fallback output, and unit tests;
the corresponding README support list remains stale. |
| crates/cli/src/external_tools.rs | Adds the Cursor Agent external-tool
variant and maps it to the `agent` executable. |
| crates/cli/tests/chef_command.rs | Adds an integration test proving
Cursor-only detection and full-auto argument forwarding through the
fake-tool fixture. |
| crates/cli/tests/support/mod.rs | Adds a selective fake-tool installer
used to isolate agent detection in integration tests. |

</details>

<sub>Reviews (1): Last reviewed commit: ["test(cli): cover chef
launching
agent"](https://github.com/helixdb/helix-db/commit/82d84586d3a6eea17822e2797e7880612753d20e)
| [Re-trigger
Greptile](https://app.greptile.com/api/retrigger?id=53606263)</sub>

**Context used:**

- Context used - readme for helixdb
([source](https://github.com/helixdb/helix-db/blob/main/README.md))
- Knowledge Base — [`helix chef`, Skills, and
Feedback](https://app.greptile.com/helixdb/-/custom-context/knowledge-base/helixdb/helix-db/-/docs/helix-cli-chef-skills.md)

<!-- /greptile_comment -->