Add python3-venv to Debian package installs

Required for creating Python virtual environments on Ubuntu/Debian.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

setup.sh

@@ -362,7 +362,7 @@ install_debian_packages() {
   export DEBIAN_FRONTEND=noninteractive
   export NEEDRESTART_MODE=a
 
-  TOTAL_STEPS=15
+  TOTAL_STEPS=16
   CURRENT_STEP=0
 
   progress "Updating APT package lists"
@@ -398,6 +398,9 @@ install_debian_packages() {
   progress "Installing gpsd"
   apt_install gpsd gpsd-clients || true
 
+  progress "Installing Python venv"
+  apt_install python3-venv || true
+
   progress "Installing dump1090"
   if ! cmd_exists dump1090; then
     apt_try_install_any dump1090-fa dump1090-mutability dump1090 || true