defs.rs: remove store/graph params, use typed memory API

resolve_placeholders() and run_agent() no longer take &Store.
All placeholders now use async memory_render/memory_links/memory_query
directly. The "siblings" placeholder uses Vec<LinkInfo> for ranking
neighbors by link_strength * node_weight.

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

src/mind/unconscious.rs

@@ -264,7 +264,7 @@ pub async fn prepare_spawn(name: &str, mut auto: AutoAgent) -> Result<SpawnResul
 
     let exclude: std::collections::HashSet<String> = std::collections::HashSet::new();
     let batch = match defs::run_agent(
-        &store, &def, def.count.unwrap_or(5), &exclude,
+        &def, def.count.unwrap_or(5), &exclude,
     ).await {
         Ok(b) => b,
         Err(e) => {