Epic: #1974

type BoxFuture<'a, T> = Pin<Box<dyn Future<Output = T> + Send + 'a>> defined in 3 files:

• zeph-memory/src/sqlite_vector_store.rs:56
• zeph-memory/src/in_memory_store.rs:13
• zeph-memory/src/vector_store.rs:58

Consolidate to single definition in zeph-memory/src/lib.rs or use futures::BoxFuture.

Acceptance Criteria:

• Single BoxFuture definition
• All 3 files use shared alias

Complexity: Trivial | Effort: 15m
Ref: TYPE-02