feat: add Dockerfile for web/worker/scheduler roles and entrypoint script

Multi-stage build: node:20 builds the SPA, python:3.12-slim runs the app.
Same image handles web, worker, scheduler roles via entrypoint.sh's first
arg. ffmpeg + unar are baked in for FC-2's transcode + archive paths.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Dockerfile

@@ -0,0 +1,44 @@
+# syntax=docker/dockerfile:1.7
+
+FROM node:20-alpine AS frontend-builder
+WORKDIR /build
+COPY frontend/package.json frontend/package-lock.json* ./
+RUN npm ci --no-audit --no-fund
+COPY frontend/ ./
+RUN npm run build
+
+FROM python:3.12-slim AS runtime
+ENV PYTHONUNBUFFERED=1 \
+    PYTHONDONTWRITEBYTECODE=1 \
+    PIP_NO_CACHE_DIR=1 \
+    PIP_DISABLE_PIP_VERSION_CHECK=1
+
+# System deps: ffmpeg (transcode + thumbnails, used in FC-2), unar (archives, FC-2),
+# libpq for psycopg, image libs.
+RUN apt-get update && apt-get install -y --no-install-recommends \
+        ffmpeg \
+        unar \
+        libpq5 \
+        libjpeg62-turbo \
+        libwebp7 \
+        libpng16-16 \
+        ca-certificates \
+    && rm -rf /var/lib/apt/lists/*
+
+WORKDIR /app
+
+COPY requirements.txt ./
+RUN pip install -r requirements.txt
+
+COPY backend/ ./backend/
+COPY alembic/ ./alembic/
+COPY alembic.ini ./
+COPY entrypoint.sh ./
+RUN chmod +x entrypoint.sh
+
+COPY --from=frontend-builder /build/dist ./frontend/dist
+
+EXPOSE 8080
+
+ENTRYPOINT ["./entrypoint.sh"]
+CMD ["web"]