Live Counter get total count per batch

SPEC.md

@@ -98,6 +98,7 @@ api: GET /api/live-video → MJPEG stream from shared-memory JPEG
 api: GET / → recounting HTML
 api: GET /api/live-progress → proxy to LIVE_API_URL:/api/current-batch
 api: GET /api/recount-progress → proxy to RECOUNT_API_URL:/api/current-batch
+api: GET /api/batch-result?file=<path> → parse `batch_NN_YYYYMMDD_HHmmSS.mp4`, query live API for count
 api: GET /api/mp4-files → [ {name, path, size, mtime} ... ]
 api: POST /api/start-recount {path} → configure go2rtc stream, return {stream_url}
 api: POST /api/stop-recount → tear down go2rtc stream