add backend-only Dockerfile for Railway deployment

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EGuUFWsH7EH7kdCv5Lu6Mw

Dockerfile.railway

@@ -0,0 +1,15 @@
+FROM python:3.11-slim
+
+COPY --from=ghcr.io/astral-sh/uv:0.9.26 /uv /uvx /bin/
+
+WORKDIR /app
+
+COPY backend/pyproject.toml backend/uv.lock ./
+
+RUN uv sync --frozen
+
+COPY backend/ .
+
+EXPOSE 5001
+
+CMD ["uv", "run", "python", "run.py"]