#151 Run the CLI test suite on Windows

Summary

• add a windows-latest CI job alongside the existing Linux job
• isolate home-directory and persisted-environment tests from the developer machine on Windows
• skip only tests whose asserted behavior is explicitly POSIX-only

Verification

• npm run typecheck
• full suite on Windows: 42 files passed, 549 tests passed, 4 skipped
• environment tests: 44 passed
• template tests: 63 passed
• setup-agent tests: 31 passed

Why

The existing CI only ran on Ubuntu, so npm shim, PowerShell argv, home resolution, and Windows process-cleanup regressions could merge unnoticed. This makes Windows a required visible check on every pull request without renaming the existing Linux check.

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Summary by cubic

Adds a Windows CI job so npm shim, PowerShell argv, and home-resolution regressions can't merge unnoticed, and makes the test suite pass on both OSes.

• Adds a test-windows job running typecheck and the full suite on windows-latest.
• Home-dependent tests set USERPROFILE alongside HOME; setup tests isolate INSTA_ENV, INSTA_API_URL, INSTA_MCP_URL, and INSTA_SKILLS_REPO.
• Adds a Windows test proving findDurableOnPath resolves a global insta.cmd while ignoring npx cache shims.
• Skips only tests asserting POSIX-only behavior (exec bits, PATH shims).
• Full suite passes on Windows: 42 files, 549 tests, 4 skipped.
• Docs name the new job and note branch protection still pins only the 1-approval rule, so a red job won't block the merge button.