feat: add containerization support

- Add Containerfile with multi-stage build for minimal image
- Add .containerignore to exclude unnecessary files
- Add /health endpoint for container health checks
- Update main.py to expose Flask app for gunicorn

Uses Python 3.12-slim base, runs as non-root user, exposes port 8000.

Containerfile

@@ -0,0 +1,51 @@
+# Build stage - install dependencies
+FROM python:3.12-slim AS builder
+
+WORKDIR /app
+
+# Install uv for fast dependency management
+COPY --from=ghcr.io/astral-sh/uv:latest /uv /usr/local/bin/uv
+
+# Copy dependency files
+COPY pyproject.toml uv.lock ./
+
+# Install production dependencies only
+RUN uv sync --frozen --no-dev --no-install-project
+
+# Runtime stage - minimal image
+FROM python:3.12-slim AS runtime
+
+WORKDIR /app
+
+# Create non-root user
+RUN useradd --create-home --shell /bin/bash appuser
+
+# Copy virtual environment from builder
+COPY --from=builder /app/.venv /app/.venv
+
+# Copy application code
+COPY src/ ./src/
+COPY migrations/ ./migrations/
+COPY alembic.ini main.py ./
+
+# Set environment variables
+ENV PATH="/app/.venv/bin:$PATH"
+ENV PYTHONUNBUFFERED=1
+ENV PYTHONDONTWRITEBYTECODE=1
+ENV FLASK_ENV=production
+
+# Create data directory and set permissions
+RUN mkdir -p /app/data && chown -R appuser:appuser /app
+
+# Switch to non-root user
+USER appuser
+
+# Expose port
+EXPOSE 8000
+
+# Health check
+HEALTHCHECK --interval=30s --timeout=10s --start-period=5s --retries=3 \
+    CMD python -c "import urllib.request; urllib.request.urlopen('http://localhost:8000/health')" || exit 1
+
+# Run with gunicorn
+CMD ["gunicorn", "--bind", "0.0.0.0:8000", "--workers", "2", "--threads", "4", "main:app"]