WIP: Agent/AgentState — 36 errors remaining, all .lock() → .state.lock() or .context.lock()

Bulk replaced Arc<Mutex<Agent>> with Arc<Agent> across all files.
Fixed control.rs, memory.rs tool handlers. Fixed oneshot Backend.
Remaining errors are all agent.lock() → agent.state.lock() or
agent.context.lock() in mind/, user/, and a few in mod.rs.

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

src/subconscious/learn.rs

@@ -330,7 +330,7 @@ pub async fn score_memories_incremental<F, Fut>(
     max_age_secs: i64,
     response_window: usize,
     client: &ApiClient,
-    agent: &std::sync::Arc<tokio::sync::Mutex<crate::agent::Agent>>,
+    agent: &std::sync::Arc<crate::agent::Agent>,
     mut on_score: F,
 ) -> anyhow::Result<usize>
 where