agents: neighborhood placeholder, organize prompt, weight-set command

Add {{neighborhood}} placeholder for agent prompts: full seed node
content + ranked neighbors (score = link_strength * node_weight) with
smooth cutoff, minimum 10, cap 25, plus cross-links between included
neighbors.

Rewrite organize.agent prompt to focus on structural graph work:
merging duplicates, superseding junk, calibrating weights, creating
concept hubs.

Add weight-set CLI command for direct node weight manipulation.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

poc-memory/src/cli/node.rs

@@ -83,6 +83,22 @@ pub fn cmd_not_useful(key: &str) -> Result<(), String> {
     Ok(())
 }
 
+pub fn cmd_weight_set(key: &str, weight: f32) -> Result<(), String> {
+    super::check_dry_run();
+    let mut store = store::Store::load()?;
+    let resolved = store.resolve_key(key)?;
+    let weight = weight.clamp(0.01, 1.0);
+    if let Some(node) = store.nodes.get_mut(&resolved) {
+        let old = node.weight;
+        node.weight = weight;
+        println!("Weight: {} {:.2} → {:.2}", resolved, old, weight);
+        store.save()?;
+    } else {
+        return Err(format!("Node not found: {}", resolved));
+    }
+    Ok(())
+}
+
 pub fn cmd_gap(description: &[String]) -> Result<(), String> {
     if description.is_empty() {
         return Err("gap requires a description".into());