feat(pgrtl): jsonb/json 컬럼을 JSON 텍스트로 읽기 (map/slice → json.Marshal)

goToHbValue 가 decoded map/slice 를 %v 대신 JSON 으로 직렬화 — jsonb 를 ::text
캐스트 없이 SELECT * 해도 PRG 에서 hb_jsonDecode 가능. 기존 ::text 경로와 일관.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

hbrtl_ext/pgrtl/pg.go

@@ -28,6 +28,7 @@ package pgrtl
 
 import (
 	"context"
+	"encoding/json"
 	"fmt"
 	"strings"
 	"sync"
@@ -283,6 +284,12 @@ func goToHbValue(g interface{}) hbrt.Value {
 		return hbrt.MakeDouble(v, 0, 0)
 	case time.Time:
 		return hbrt.MakeString(v.Format(time.RFC3339))
+	case map[string]interface{}, []interface{}:
+		// jsonb/json columns arrive as decoded maps/slices — render as JSON
+		// text (matches the `col::text` read convention; callers hb_jsonDecode).
+		if b, err := json.Marshal(v); err == nil {
+			return hbrt.MakeString(string(b))
+		}
 	}
 	return hbrt.MakeString(fmt.Sprintf("%v", g))
 }