feat(docker): add Docker support and env example

Dockerfile

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+FROM python:3.12-slim
+
+# Prevent .pyc files and enable unbuffered stdout/stderr
+ENV PYTHONDONTWRITEBYTECODE=1 \
+    PYTHONUNBUFFERED=1
+
+WORKDIR /app
+
+# Install deps first — layer cache reuse on code-only changes
+COPY requirements.txt .
+RUN pip install --no-cache-dir -r requirements.txt
+
+# Copy source
+COPY main.py config.py ./
+COPY modules/ modules/
+
+# Run as non-root
+RUN adduser --disabled-password --gecos "" botuser && \
+    mkdir -p /app/storage /app/logs && \
+    chown -R botuser:botuser /app
+
+USER botuser
+
+# Persistent volume for Pyrogram session and logs
+VOLUME ["/app/storage", "/app/logs"]
+
+CMD ["python", "main.py"]