worker を追加（yt-dlp によるダウンロード、段階別進捗、ffprobe 検査、実行中の取り消し）

Dockerfile.worker

@@ -0,0 +1,21 @@
+FROM golang:1.27.1-alpine AS build
+
+WORKDIR /src
+COPY go.mod go.sum ./
+RUN go mod download
+COPY cmd ./cmd
+COPY internal ./internal
+RUN CGO_ENABLED=0 go build -trimpath -ldflags="-s -w" -o /worker ./cmd/worker
+
+FROM python:3.13-slim
+ARG YT_DLP_VERSION=2026.08.19
+RUN apt-get update \
+    && apt-get install -y --no-install-recommends ca-certificates ffmpeg tzdata \
+    && pip install --no-cache-dir "yt-dlp[default]==${YT_DLP_VERSION}" \
+    && rm -rf /var/lib/apt/lists/*
+WORKDIR /app
+COPY --from=build /worker /app/worker
+ENV HOME=/tmp \
+    XDG_CACHE_HOME=/tmp/yt-dlp-cache
+USER 65532:65532
+ENTRYPOINT ["/app/worker"]