persy v0.2.1 — contributing-to-persy skill

Added

• contributing-to-persy skill — a contributor/maintainer playbook for
  working a GitHub issue: triage → green baseline → reproduce test-first → minimal
  fix → full suite → CHANGELOG → PR. Encodes persy's architecture invariants
  (provider ABC, frozen snapshot, append-only episodic, atomic state) and the
  public-repo hard rules (no .persy/, no machine paths, no secrets/PII, keep
  versions synced, keep mempalace lazy). Registered in persy.config.json.