feat: [file] path 기반 presigned URL 엔드포인트 추가

- POST /api/v1/files/presigned-url-by-path 추가
- file_id 없이 image_path만 있는 레거시 데이터 지원

app/Http/Controllers/Api/V1/FileStorageController.php

@@ -145,6 +145,21 @@ public function presignedUrl(int $id, Request $request)
         return ApiResponse::handle(fn () => ['url' => $url]);
     }
 
+    /**
+     * R2 Presigned URL 발급 (file_path 기반, 30분 유효)
+     */
+    public function presignedUrlByPath(Request $request)
+    {
+        $path = $request->input('path');
+        if (! $path) {
+            abort(400, 'path is required');
+        }
+
+        $url = Storage::disk('r2')->temporaryUrl($path, now()->addMinutes(30));
+
+        return ApiResponse::handle(fn () => ['url' => $url]);
+    }
+
     /**
      * Soft delete file
      */