v4.2.0 — Explain WHY, token budgets, version supersession, negative memories

Added

• Explain WHY — memory_recall / memory_smart_recall explain: true appends a deterministic reason line (↳ 100% relevance · used 14× · used today · importance HIGH)
• Token budgets — budget_tokens param drops the tail of the recall that would exceed the estimate
• Version supersession — memory_consolidate mode: "versions" marks older library-version entries obsolete in favor of the newest
• Negative memories — new warning category recalled with +0.2 boost
• Extended stats — memory_stats reports Hit rate, Duplicate % and Dead %
• Ranking factors — language-family (+0.1) and path_scope folder-match (+0.05) boosts

340 tests passing.