Add complete POP3 to Gmail forwarder implementation

Co-authored-by: christianlouis <361235+christianlouis@users.noreply.github.com>

Dockerfile

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+FROM python:3.11-slim
+
+# Set working directory
+WORKDIR /app
+
+# Install dependencies
+COPY requirements.txt .
+RUN pip install --no-cache-dir -r requirements.txt
+
+# Copy application code
+COPY pop3_forwarder.py .
+
+# Create non-root user for security
+RUN useradd -m -u 1000 forwarder && \
+    chown -R forwarder:forwarder /app
+
+USER forwarder
+
+# Run the application
+CMD ["python", "-u", "pop3_forwarder.py"]