Remove Store::cached(), consolidate on access_local()

- Remove CACHED_STORE, cached(), is_stale(), set_store() - redundant
- Convert all Store::cached() callers to use access_local()
- Single Store::load() call remains in access() fallback path

All store access now goes through hippocampus::access() / access_local(),
which handles socket connection or local fallback with caching.

Co-Authored-By: Proof of Concept <poc@bcachefs.org>

src/agent/tools/memory.rs

@@ -1,7 +1,7 @@
 // tools/memory.rs — Native memory graph operations
 //
-// Daemon: calls set_store() at startup for direct store access.
-// Clients: lazy init tries socket, falls back to local store.
+// Access via hippocampus::access() / access_local(). Clients try socket
+// first, fall back to local store.
 
 #![allow(unused_variables)] // macro-generated args for no-param tools
 
@@ -17,7 +17,7 @@ pub use crate::hippocampus::{
     journal_tail, journal_new, journal_update,
     graph_topology, graph_health, graph_communities, graph_normalize_strengths,
     graph_link_impact, graph_hubs, graph_trace,
-    set_store, socket_path,
+    socket_path,
 };
 
 // ── Macro for generating tool wrappers ─────────────────────────