v10.20.0 phase 0.5 removed; Nyx is namespace-scoped

Removed

• Phase 0.5 (Cemelify) no longer exists in the Nyx cycle. Rewriting
  already-stored memories every night is generation against content
  whose fidelity is the product: it drifted exact strings on weaker
  models, was disabled on every known deployment, and ran ungated by
  the phase list, so a zero-LLM --phases 1,2,4,6 run on a
  key-configured host still fired LLM calls (observed in the field:
  28x 401 against a stale key). MNEMOS_NYX_CEMELIFY is gone;
  cemelify() itself remains for ingest-time shaping of NEW content.
  Stored content is never rewritten in place.

Fixed

• Nyx loaders are namespace-scoped: load_embeddings and
  load_memory_meta read only the active namespace (default: the same
  resolution as every write path; both accept an explicit namespace=).
  Since v10.6.0 the write side was namespace-correct but reads saw every
  namespace in the DB file, so on a multi-tenant deployment phase 2
  could cluster tenant A's memories with tenant B's, merge them into
  the current namespace and archive both originals. Found in the field
  on a second deployment; single-namespace stores were never affected.