move memory_search from hippocampus to subconscious/hook

memory_search.rs is agent orchestration (surface-observe, journal,
reflect cycles), not memory storage. Rename to hook.rs and move to
subconscious/ where it belongs.

Backward compat: pub use subconscious::hook as memory_search in lib.rs
so existing crate::memory_search paths still resolve.

src/hippocampus/mod.rs

@@ -17,4 +17,3 @@ pub mod neuro;
 pub mod counters;
 pub mod migrate;
 pub mod transcript;
-pub mod memory_search;