render: extract render_node() + add {{seed}} placeholder

Refactor cmd_render into render_node() that returns a String —
reusable by both the CLI and agent placeholders.

Add {{seed}} placeholder: renders each seed node using the same
output as poc-memory render (content + deduped footer links). Agents
see exactly what a human sees — no special formatting.

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

poc-memory/src/agents/defs.rs

@@ -164,6 +164,21 @@ fn resolve(
             })
         }
 
+        // seed — render output for each seed node (content + deduped links)
+        "seed" => {
+            let mut text = String::new();
+            let mut result_keys = Vec::new();
+            for key in keys {
+                if let Some(rendered) = crate::cli::node::render_node(store, key) {
+                    if !text.is_empty() { text.push_str("\n\n---\n\n"); }
+                    text.push_str(&format!("## {}\n\n{}", key, rendered));
+                    result_keys.push(key.clone());
+                }
+            }
+            if text.is_empty() { return None; }
+            Some(Resolved { text, keys: result_keys })
+        }
+
         "organize" => {
             // Show seed nodes with their neighbors for exploratory organizing
             use crate::store::NodeType;