feat(T06): deployment config - Dockerfiles, docker-compose, Coolify guide, env example

backend/Dockerfile

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+# ERP Nutzfahrzeuge — Backend Dockerfile
+# Python 3.13-slim + FastAPI + uvicorn
+# System packages: WeasyPrint (libpango, libcairo), Pillow (libjpeg, libpng)
+
+FROM python:3.13-slim AS base
+
+# --- System packages for WeasyPrint and Pillow ---
+RUN apt-get update && apt-get install -y --no-install-recommends \
+    libpango-1.0-0 \
+    libpangoft2-1.0-0 \
+    libcairo2 \
+    libgdk-pixbuf2.0-0 \
+    libjpeg62-turbo \
+    libpng16-16 \
+    libffi-dev \
+    curl \
+    && rm -rf /var/lib/apt/lists/*
+
+# --- Python venv ---
+RUN python -m venv /opt/venv
+ENV PATH="/opt/venv/bin:$PATH"
+ENV PYTHONDONTWRITEBYTECODE=1
+ENV PYTHONUNBUFFERED=1
+
+WORKDIR /app
+
+# --- Install dependencies first (better layer caching) ---
+COPY requirements.txt .
+RUN pip install --no-cache-dir -r requirements.txt
+
+# --- Copy application code ---
+COPY . .
+
+# --- Create upload and contract directories ---
+RUN mkdir -p /data/uploads /tmp/contracts
+
+# --- Expose port ---
+EXPOSE 8000
+
+# --- Health check ---
+HEALTHCHECK --interval=30s --timeout=5s --retries=3 --start-period=10s \
+    CMD curl -f http://localhost:8000/api/v1/health || exit 1
+
+# --- Start command ---
+CMD ["python", "-m", "uvicorn", "app.main:app", "--host", "0.0.0.0", "--port", "8000", "--workers", "4"]