memory: add spreading activation tool

Add `poc-memory graph spread` command that takes multiple seed node keys,
runs spreading activation through the graph, and returns nodes ranked by
total activation — nodes that bridge multiple seed concepts score highest.

Expose spreading_activation() as pub from the query engine. Add
memory_spread and memory_search_content tool definitions for MCP.

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

src/cli/graph.rs

@@ -6,6 +6,7 @@
 // trace, spectral-*, organize, interference.
 
 use crate::{store, graph, neuro, spectral};
+use crate::store::StoreView;
 
 pub fn cmd_graph() -> Result<(), String> {
     let store = store::Store::load()?;
@@ -109,6 +110,45 @@ pub fn cmd_normalize_strengths(apply: bool) -> Result<(), String> {
     Ok(())
 }
 
+pub fn cmd_spread(keys: &[String], max_results: usize) -> Result<(), String> {
+    if keys.is_empty() {
+        return Err("spread requires at least one seed key".into());
+    }
+
+    let store = store::Store::load()?;
+    let graph = graph::build_graph_fast(&store);
+    let params = store.params();
+
+    let seeds: Vec<(String, f64)> = keys.iter()
+        .filter_map(|k| {
+            let resolved = store.resolve_key(k).ok()?;
+            Some((resolved, 1.0))
+        })
+        .collect();
+
+    if seeds.is_empty() {
+        return Err("no valid seed keys found".into());
+    }
+
+    let results = crate::search::spreading_activation(
+        &seeds, &graph, &store,
+        params.max_hops, params.edge_decay, params.min_activation,
+    );
+
+    let seed_keys: std::collections::HashSet<&str> = seeds.iter()
+        .map(|(k, _)| k.as_str())
+        .collect();
+
+    for (key, score) in results.iter()
+        .filter(|(k, _)| !seed_keys.contains(k.as_str()))
+        .take(max_results)
+    {
+        println!("  {:.2}  {}", score, key);
+    }
+
+    Ok(())
+}
+
 pub fn cmd_link(key: &[String]) -> Result<(), String> {
     if key.is_empty() {
         return Err("link requires a key".into());