Add backend pipeline Dockerfile with lightweight deps

backend/Dockerfile

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+FROM python:3.11-slim
+
+WORKDIR /app
+
+# Install system dependencies for newspaper3k and psycopg2
+RUN apt-get update && apt-get install -y --no-install-recommends \
+    gcc \
+    libxml2-dev \
+    libxslt1-dev \
+    libjpeg-dev \
+    zlib1g-dev \
+    libpq-dev \
+    && rm -rf /var/lib/apt/lists/*
+
+# Install Python dependencies
+COPY requirements-pipeline.txt ./requirements.txt
+RUN pip install --no-cache-dir -r requirements.txt
+
+# Download NLTK data needed by newspaper3k
+RUN python -c "import nltk; nltk.download('punkt_tab', quiet=True)"
+
+# Copy application code
+COPY . .
+
+CMD ["python", "run_pipeline.py"]