enhance: Support non-sudo operation for libvirt users

[williamzujkowski]

Problem

Scripts use `sudo` for all virsh/virt-install commands, but users in the `libvirt` group can run these without sudo via socket activation.

Current Behavior

# In virt_install_agent_vm.sh
local cmd=(
    sudo virt-install  # <-- unnecessary for libvirt group members
    ...
)

Proposed Solution

1. Auto-detect if user can run libvirt commands without sudo:

can_run_without_sudo() {
    virsh list >/dev/null 2>&1
}

SUDO=""
if ! can_run_without_sudo; then
    SUDO="sudo"
fi

2. Or add a --no-sudo flag for users who know they don't need it

3. Update documentation to explain libvirt group membership

Benefits

• Works in environments where sudo requires a password
• Cleaner for users already configured for libvirt access
• Better for CI/CD automation

Files to Update

• virt_install_agent_vm.sh
• snapshot_manager.sh
• README.md (add libvirt group setup instructions)

Related

Blocking issue during E2E testing