PiMem v1.3.1

PiMem v1.3.1 is a retrieval-boundary and reproducibility hardening release.\n\nHighlights:\n- Fall back from Qdrant to exact SQLite dense retrieval only for typed availability failures. Configuration, generation, scope, and provenance failures remain visible and fail closed.\n- Record dense fallback usage and result-affecting HNSW settings in retrieval metadata and formal runtime identities.\n- Pin the complete Qdrant configuration in protected MemoryAgentBench YAML, preventing ambient environment drift.\n- Separate SQLite lexical query planning from the persistence facade and require explicit dense-retriever injection in hybrid composition.\n- Strengthen bounded-context architecture tests and remove internal imports through public barrels.\n\nValidation:\n- TypeScript: 344 tests passed\n- Python integrations: 191 tests passed\n- Typecheck, generated architecture catalog verification, and production build passed