Unconscious agents: persistent AutoAgent, shared Agent Arc for UI

- AutoAgent stored on UnconsciousAgent, swapped out for runs, restored
  on completion (same pattern as subconscious agents)
- Agent Arc created before spawn and stored on UnconsciousAgent so
  the TUI can lock it to read conversation context live
- run_shared() method on AutoAgent for running with a pre-created Agent
- Default tools: memory_tools (not memory_and_journal_tools)
- trigger/spawn_agent made async for Agent::new()

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

src/agent/oneshot.rs

@@ -149,6 +149,16 @@ impl AutoAgent {
         self.run_with_backend(&mut backend, bail_fn).await
     }
 
+    /// Run using a pre-created agent Arc. The caller retains the Arc
+    /// so the UI can lock it to read entries live.
+    pub async fn run_shared(
+        &mut self,
+        agent: &std::sync::Arc<Agent>,
+    ) -> Result<String, String> {
+        let mut backend = Backend(agent.clone());
+        self.run_with_backend(&mut backend, None).await
+    }
+
     /// Run forked using a shared agent Arc. The UI can lock the same
     /// Arc to read entries live during the run.
     pub async fn run_forked_shared(