Consolidate Qdrant access through VectorStore trait #844
Description
Context
Four crates (zeph-memory, zeph-skills, zeph-mcp, zeph-index) depend directly on qdrant-client with slightly different access patterns.
Solution
Route all Qdrant operations through zeph-memory's VectorStore trait to reduce coupling and enable alternative vector backends.
Acceptance Criteria
- Only zeph-memory depends on qdrant-client directly
- Other crates use VectorStore trait
- Tests pass
Epic: #832 | Effort: L | Crate: zeph-memory, zeph-skills, zeph-mcp, zeph-index
Critical path: after AR-006/AR-007/AR-008 (stable trait boundaries needed)