Fuzzy search over the graph — substring + qualified-path match with
deterministic ranking. Wraps GraphStore::lookup_symbol(fuzzy=true) and
a list_all_nodes scan to also match on qualified_name, then ranks.
Guided-tour generation — deterministic graph traversal that picks the
“important” symbols of a repo (or of a seeded subgraph) and orders them so
a reader can walk through the codebase top-down.