feat: add backend Dockerfile and requirements

backend/Dockerfile

@@ -0,0 +1,14 @@
+FROM python:3.12-slim
+
+WORKDIR /app
+
+RUN apt-get update && apt-get install -y --no-install-recommends \
+    gcc libpq-dev \
+    && rm -rf /var/lib/apt/lists/*
+
+COPY requirements.txt .
+RUN pip install --no-cache-dir -r requirements.txt
+
+COPY . .
+
+CMD ["sh", "-c", "alembic upgrade head && uvicorn app.main:app --host 0.0.0.0 --port 8000"]