chore: add root Dockerfile for Hugging Face Spaces deployment

Dockerfile

@@ -0,0 +1,30 @@
+FROM python:3.11-slim
+
+# Set the working directory
+WORKDIR /app
+
+# Install system dependencies if any are needed
+RUN apt-get update && apt-get install -y --no-install-recommends \
+    build-essential \
+    && rm -rf /var/lib/apt/lists/*
+
+# Copy backend requirements first to leverage Docker cache
+COPY backend/requirements.txt .
+
+# Install python dependencies
+RUN pip install --no-cache-dir -r requirements.txt
+
+# Copy backend codebase
+COPY backend/ ./backend/
+
+# Create data directories and set permissions so Hugging Face user can write to them
+RUN mkdir -p /app/backend/data/sources && chmod -R 777 /app/backend/data
+
+# Set PYTHONPATH so Python can locate our backend module
+ENV PYTHONPATH=/app
+
+# Expose Hugging Face Spaces default port
+EXPOSE 7860
+
+# Run uvicorn on port 7860
+CMD ["uvicorn", "backend.main:app", "--host", "0.0.0.0", "--port", "7860"]