Convert store and CLI to anyhow::Result for cleaner error handling

Replace Result<_, String> with anyhow::Result throughout:
- hippocampus/store module (persist, ops, types, view, mod)
- CLI modules (admin, agent, graph, journal, node)
- Run trait in main.rs

Use .context() and .with_context() instead of .map_err(|e| format!(...))
patterns. Add bail!() for early error returns.

Add access_local() helper in hippocampus/mod.rs that returns
Result<Arc<Mutex<Store>>> for direct local store access.

Fix store access patterns to properly lock Arc<Mutex<Store>> before
accessing fields in mind/unconscious.rs, mind/mod.rs, subconscious/learn.rs,
and hippocampus/memory.rs.

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

src/hippocampus/memory.rs

@@ -19,7 +19,8 @@ pub struct MemoryNode {
 impl MemoryNode {
     /// Load a node from the store by key.
     pub fn load(key: &str) -> Option<Self> {
-        let store = Store::load().ok()?;
+        let arc = super::access_local().ok()?;
+        let store = arc.try_lock().ok()?;
         Self::from_store(&store, key)
     }