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).

internal/brain/rank/rank.go

@@ -7,14 +7,22 @@ import (
 	"strings"
 )
 
+type HopNode struct {
+	ID    string `json:"id"`
+	Label string `json:"label"`
+	Name  string `json:"name"`
+	Depth int    `json:"depth"`
+}
+
 // Hit is one search result, mirroring the python script's dict shape.
 type Hit struct {
-	ID      string  `json:"id"`
-	Text    string  `json:"text"`
-	Root    string  `json:"root"`
-	Source  string  `json:"-"`
-	Score   float64 `json:"score"`
-	Snippet string  `json:"snippet,omitempty"`
+	ID      string    `json:"id"`
+	Text    string    `json:"text"`
+	Root    string    `json:"root"`
+	Source  string    `json:"-"`
+	Score   float64   `json:"score"`
+	Snippet string    `json:"snippet,omitempty"`
+	Hops    []HopNode `json:"hops,omitempty"`
 }
 
 // rrfK dampens the contribution of low ranks; same constant as kblib.py.