MemoryNode moved from agent/memory.rs to hippocampus/memory.rs — it's
a view over hippocampus data, not agent-specific.
Store operations (set_weight, set_link_strength, add_link) moved into
store/ops.rs. CLI code (cli/graph.rs, cli/node.rs) and agent tools
both call the same store methods now. render_node() delegates to
MemoryNode::from_store().render() — 3 lines instead of 40.
Co-Authored-By: Proof of Concept <poc@bcachefs.org>
