Epic 3: VectorStore Trait Abstraction (M28)

[bug-ops]

Problem

QdrantStore is hardcoded in SemanticMemory. Adding an alternative backend (pgvector, in-memory, Milvus) requires rewriting SemanticMemory.

Solution

Extract a VectorStore trait, make QdrantStore implement it, change SemanticMemory to hold Option<Box<dyn VectorStore>>.

Issues

• feat(memory): extract VectorStore trait #462 feat(memory): extract VectorStore trait size/M
• refactor(memory): make QdrantStore implement VectorStore #463 refactor(memory): make QdrantStore implement VectorStore size/M
• feat(memory): in-memory VectorStore for testing #464 feat(memory): in-memory VectorStore for testing size/S
• refactor(memory): SemanticMemory generic over VectorStore #465 refactor(memory): SemanticMemory generic over VectorStore size/M

Verification

Run unit tests with InMemoryVectorStore instead of Qdrant testcontainers; swap backend in config.