Path capability probe

Throwaway repo for Effect issue EFF-2776: what can Node, Bun and Deno do with filenames that are not valid Unicode (POSIX non-UTF-8 bytes, Windows unpaired surrogates), per filesystem operation?

• probe.mjs — the probe. node probe.mjs, bun probe.mjs, deno run -A probe.mjs.
• oracle.py — independent fixture creator/lister (Python bytes paths / wide-char API).
• aggregate.mjs — merges results-*.json artifacts into one matrix.
• .github/workflows/probe.yml — runs the probe on ubuntu/macos/windows × node20/22/24, bun, deno.