Create Dockerfile and .dockerignore for upcoming official docker support

- Update .gitignore

Dockerfile

@@ -0,0 +1,22 @@
+# Base image (multi-arch via buildx)
+FROM python:3.10-slim
+
+# Prevents pyc files + enables unbuffered logging
+ENV PYTHONDONTWRITEBYTECODE=1 \
+    PYTHONUNBUFFERED=1
+
+# Install dependencies
+WORKDIR /app
+COPY requirements.txt .
+RUN pip install --no-cache-dir -r requirements.txt
+
+# Copy only necessary files (via .dockerignore)
+COPY . .
+
+# Create non-root user
+RUN adduser --disabled-password --no-create-home --gecos "" appuser \
+    && chown -R appuser /app
+USER appuser
+
+# Default command
+ENTRYPOINT ["python", "src/main.py"]