Support linked npm workflows with persistent WASI symlinks

[noise64]

• resolves GOL-388
• replaces runtime-local symlink placeholders with persistent relative WASI filesystem symlinks shared across fresh execution runtimes
• enables local npm exec, npx, workspace links, npm link, registry-acquired bins, and representative pnpm-style package layouts
• preserves linked CommonJS package identity while keeping module-resolution candidate probing on direct filesystem checks
• rejects rooted symlink targets atomically with EINVAL, and documents the production, macOS/Linux, and Windows privilege boundaries
• adds P2/P3 filesystem, execution, npm workflow, module identity, broken-link, cycle, rename, and unlink coverage
• stacked on Run npm package-management workflows inside wasm-rquickjs #125; rebase onto main after that PR merges
• TODO: GOL-427 tracks Windows linked workflows without Developer Mode or equivalent symlink privilege

Node compatibility

• primary CI-enforced: 3217/4391 (73.3%) → 3206/4391 (73.0%)
• full public: 3217/5750 (55.9%) → 3206/5750 (55.8%)
• fs: 373 passing / 12 gaps → 369 passing / 16 gaps
• module: 129 passing / 25 gaps → 122 passing / 32 gaps
• the passing inventory decreases because 11 vendored tests require rooted symlink targets that WASI cannot honestly provide; persistent relative-link behavior is covered by focused runtime tests instead