cleanup: remove dead placeholder code, use RPC for identity loading

- links() in memory.rs: use cached_store() instead of MemoryNode::load()
- identity.rs: use memory_rpc for Store context loading
- defs.rs: delete dead placeholders (topology, nodes/episodes, health, split)
  - agents now use {{tool: graph_topology}} etc instead
- prompts.rs: delete unused format_split_plan_node()

Co-Authored-By: Kent Overstreet <kent.overstreet@linux.dev>

src/mind/identity.rs

@@ -92,10 +92,15 @@ fn load_memory_files(memory_project: Option<&Path>, context_groups: &[ContextGro
                 continue;
             }
             ContextSource::Store => {
-                // Load from the memory graph store
+                // Load from the memory graph store via RPC
                 for key in &group.keys {
-                    if let Some(node) = crate::hippocampus::memory::MemoryNode::load(key) {
-                        memories.push((key.clone(), node.content));
+                    if let Ok(content) = crate::mcp_server::memory_rpc(
+                        "memory_render",
+                        serde_json::json!({"key": key, "raw": true}),
+                    ) {
+                        if !content.trim().is_empty() {
+                            memories.push((key.clone(), content));
+                        }
                     }
                 }
             }