docs(test): note why build_vite_env has no Windows skip

Fixture-only change; also exercises the native-cache fix: this commit
must reuse the NAPI binding cache, not rebuild it.

Claude-Session: https://claude.ai/code/session_01NRgjMi2Vus3iJctudGEWPT

Author: fengmk2

crates/vite_cli_snapshots/tests/cli_snapshots/fixtures/build_vite_env/snapshots.toml

@@ -1,3 +1,6 @@
+# No skip-platforms here on purpose: the legacy case skipped win32, but the
+# reasons (shell env prefixes, eol-dependent content hashes) do not apply in
+# this runner, and the Windows CI job has validated the case since.
 [[case]]
 name = "build_vite_env"
 vp = "local"