Added a typed scan function: walks the live nodes once, skips
transparent layers, keeps only entries whose node_type matches the
filter, sorts the survivors by salience, paginates. Header forward
decl in el_runtime.h so callers can find it.
Empty / NULL filter falls through to engram_scan_nodes_json so the
existing GET /api/nodes contract is preserved exactly.
This is what every list-X tool in the MCP wrapper has been wanting:
listProcesses returning only Process nodes, not all of them, without
the wrapper having to fetch + filter client-side.
Will Anderson
276c0e5997