feat: search --hop walks FROM_FILE to Person. (#30)

Parser no longer errors; hop 1 returns File, hop 3 reaches Person.
Rebuild writes Leaf-[:FROM_FILE]->File so the walk is not empty
on a fresh index (Gitea #17).

bin/brain/search.go

@@ -3,7 +3,7 @@
 //
 // bin/brain/search.go - deduction search over the 2dph brain.
 //
-//	./bin/brain/search.go "query" [--root facts|info] [--repo P] [-n N] [--json] [--no-web]
+//	./bin/brain/search.go "query" [--root facts|info] [--repo P] [-n N] [--hop N] [--json] [--no-web]
 //	./bin/brain/search.go serve [port]
 //	./bin/brain/search.go --list-model
 //