Fix Linux Mint Docker repository detection in lib/system.sh

- Replace Docker convenience script with manual repository setup in lib/system.sh
- Add proper Ubuntu codename detection for Linux Mint using UBUNTU_CODENAME from /etc/os-release
- Include fallback version mapping for older Linux Mint versions (22.x->noble, 21.x->jammy, 20.x->focal)
- Add debug output to track codename detection
- Resolves issue where get.docker.com script was using incorrect "xia" codename instead of "noble"

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

privileged-setup

@@ -69,6 +69,7 @@ install_docker() {
         ubuntu_codename=$(lsb_release -cs)
     fi
     
+    echo "DEBUG: Detected OS: $(lsb_release -is), Ubuntu codename: $ubuntu_codename"
     echo "deb [arch=$(dpkg --print-architecture) signed-by=/usr/share/keyrings/docker-archive-keyring.gpg] https://download.docker.com/linux/ubuntu $ubuntu_codename stable" | tee /etc/apt/sources.list.d/docker.list > /dev/null
     
     # Update package index with Docker packages