store: remove visit tracking infrastructure

Remove AgentVisit, TranscriptSegment, and all related visit tracking code.
Provenance is what we've been using to track agent interaction with nodes.

Also removes dead fields from Node (state_tag, created).

-349 lines.

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

src/agent/oneshot.rs

@@ -7,7 +7,7 @@
 // Also contains the legacy run_one_agent() pipeline and process
 // management for spawned agent subprocesses.
 
-use crate::store::{self, Store};
+use crate::store;
 use crate::subconscious::{defs, prompts};
 
 use std::collections::HashMap;
@@ -382,7 +382,6 @@ pub struct AgentResult {
 /// Run an agent. If keys are provided, use them directly (bypassing the
 /// agent's query). Otherwise, run the query to select target nodes.
 pub async fn run_one_agent(
-    store: &mut Store,
     agent_name: &str,
     count: usize,
     keys: Option<&[String]>,
@@ -413,11 +412,7 @@ pub async fn run_one_agent(
                 phase: step.phase.clone(),
             });
         }
-        let batch = prompts::AgentBatch { steps: resolved_steps, node_keys: all_keys };
-        if !batch.node_keys.is_empty() {
-            store.record_agent_visits(&batch.node_keys, agent_name).ok();
-        }
-        batch
+        prompts::AgentBatch { steps: resolved_steps, node_keys: all_keys }
     } else {
         let effective_count = def.count.unwrap_or(count);
         defs::run_agent(&def, effective_count, &Default::default()).await?