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/subconscious/mod.rs

@@ -13,8 +13,10 @@
 //   enrich       — journal enrichment, experience mining
 //   digest       — episodic digest generation (daily/weekly/monthly)
 //   daemon       — background job scheduler
+//   hook         — session hook: context injection, agent orchestration
 //   transcript   — shared JSONL transcript parsing
 
+pub mod hook;
 pub mod transcript;
 pub mod api;
 pub mod llm;