Update Dockerfile to include python-is-python3 and enhance entrypoint script for conditional package list updates based on network availability.

Dockerfile

@@ -24,14 +24,13 @@ RUN apt update && apt install -y \
         # Packet analysis tools
         tshark \
         # Programming languages and runtimes
-        python3 python3-pip python3-venv python3-dev \
+        python3 python3-pip python3-venv python3-dev python-is-python3 \
         # Development tools
         software-properties-common build-essential \
         # Remote access
         openssh-server \
         # Localization
         locales
-    # Note: Keeping apt cache for dev convenience
 
 # Install Node.js using official NodeSource repository
 RUN curl -fsSL https://deb.nodesource.com/setup_lts.x | sudo -E bash - && \