feat: [file] API Resource에서 image_url (presigned URL) 반환

- File 모델에 presignedUrl() 메서드 추가
- GuiderailModelResource: image_url + components[].image_url 반환
- BendingItemResource: image_url 반환
- 소비자(MNG, React)가 별도 처리 없이 R2 직접 로드 가능

app/Models/Commons/File.php

@@ -98,6 +98,21 @@ public function fileable()
         return $this->morphTo();
     }
 
+    /**
+     * R2 Presigned URL 생성 (30분 유효)
+     */
+    public function presignedUrl(int $minutes = 30): ?string
+    {
+        if (! $this->file_path) {
+            return null;
+        }
+
+        return Storage::disk('r2')->temporaryUrl(
+            $this->file_path,
+            now()->addMinutes($minutes)
+        );
+    }
+
     /**
      * Get the full storage path
      */