test(windows): Windows MSVC test suite fails on main #4861

Problem

The Windows MSVC `PR lint and test` job fails 12 tests on main on both x64 and arm64 (for example run 39803394167 on #4288). The job only runs on PRs labeled `test:windows`, so the failures went unnoticed.

Failures

• Unix socket path validation (5 tests in openshell-core, openshell-server, openshell-supervisor): `Path::is_absolute()` rejects POSIX paths such as `/run/backend.sock` on Windows, producing `invalid boundary control transport endpoint`.
• Supervisor baseline write-back (5 `startup_policy_write_refusal_*` tests): proxy baseline paths (`/usr`, `/tmp`, ...) do not exist on Windows, so enrichment adds nothing and there is no write-back to refuse.
• `sqlite_concurrent_writes_return_their_own_resource_version`: slow FULL-sync commits on Windows runners starve a writer past the 5s SQLite busy timeout (`database is locked`).
• `random_scope_mix_never_deadlocks`: Windows rounds 1-2 ms `tokio::time::sleep` holds up to ~16 ms, so the mix exceeds its 20s deadline.