Introduce the VectorStore domain model as a foundation for multi-store
vector DB architecture (Phase 1, PR 1/4).
- VectorStore entity with ConnectionConfig (AES-GCM encrypted) and IndexConfig
- VectorStoreRepository interface and GORM implementation (CRUD + duplicate check)
- PostgreSQL migration (000031) and SQLite migration (000001)
- Unit tests for types, encryption, validation, and helpers
ochan.kwon