Experiment: pg-fs persistence probe (local only)

[nkarpov]

Summary

Experimental spike to evaluate PostgreSQL/Lakebase-backed persistence via pg-fs.

This PR intentionally adds a local probe only (no runtime wiring yet) so we can keep a reference implementation and benchmark path in the repo.

Included

• scripts/pgfs-probe.mjs
  • commands: push, pull, list, bench
  • env-configured include/exclude globs
  • manifest-driven restore model
• npm run pgfs:probe -- <command>
• README section for local usage
• .gitignore update for local env files (.env, .env.local)

Safety / hygiene

• No credentials committed
• No runtime session data committed
• Connection string is expected only via local env (PGFS_DATABASE_URL)

Notes from spike

• pg-fs was not fully plug-and-play in our environment (schema bootstrap/index behavior required manual investigation during testing).
• This is not production-ready persistence yet; it is an experiment artifact for iteration.