v0.5.2 — elaborations refine memory instead of replacing it

• Background learning now refines instead of replaces when a later turn merely elaborates an existing memory: same memory id, growing observation chain, untouched validity window, zero rows superseded (issue #34).
• The extraction prompt proposes an unmarked supersede for non-contradictory elaborations so the deterministic refine route applies the detail in place; explicit corrections keep the existing supersede behavior.
• Declined refine cases fall through to the prior create-plus-supersede path unchanged; the refine primitive is idempotent under replay.
• Dev corpus: new elaboration-refine golden scenario locks the route in; the subtle-supersession scripted replacement turn now marks itself an explicit correction.