* fix: return metadata in recall responses (#674)
Metadata stored during retain was never retrieved during recall.
Add metadata to all SQL SELECT queries, the RetrievalResult dataclass,
ScoredResult.to_dict(), and MemoryFact construction in the recall pipeline.
* test: add metadata round-trip test for retain→recall
Replace placeholder metadata test with one that actually passes
metadata via retain_batch_async and asserts it is returned on recall.
* fix: parse metadata JSON string from database in MemoryFact
asyncpg may return JSONB columns as strings. Add a field_validator
to MemoryFact.metadata to handle JSON string deserialization.
0bcbf8491b