add Node/TypeScript SDK (@iicky/murk-secrets)

[iicky]

• napi-rs bindings in node/ workspace crate
• Cargo workspace: murk-cli (root) + murk-napi (node/)
• API: load(), get(), exportAll(), hasKey(), Vault class
• auto-generated TypeScript definitions
• 13 Node tests
• CI workflow: test on PRs, build native binaries + publish to npm on tags
• cross-platform: macOS (x64, arm64), Linux (x64, arm64, musl), Windows

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 52.57%. Comparing base (e1adb9c) to head (90b10a4).
⚠️ Report is 11 commits behind head on main.
✅ All tests successful. No failed tests found.

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