ci: run Rust tests in desktop gate

[fly1d]

Summary

• replace duplicated Rust commands in the Desktop workflow with npm run desktop:check
• ensure the two Rust provider security tests execute on the macOS CI runner
• keep local and CI desktop gates defined in one place

Verification

• npm run desktop:check (2 Rust tests passed)
• workflow YAML parsed successfully
• diff check passed

[fly1d]

Reviewed the complete diff. The desktop workflow now delegates to the shared desktop:check script, which adds the Rust test suite while retaining fmt, Clippy, and compilation checks. The workflow file is also included in both pull_request and push path filters. CI, browser smoke, CodeQL, and the macOS desktop gate all pass. No blocking findings.