Fix apt-ostree container installation failure

- Enhanced check_systemd() function to properly detect container environments
- Added detection for Docker, Podman, and other container runtimes
- Verify systemd is running as PID 1 before attempting service operations
- Check systemd D-Bus availability before service configuration
- Gracefully skip systemd setup in containers with helpful messages
- Provide manual configuration instructions for real systems

Fixes container builds and CI/CD pipelines that install apt-ostree
while maintaining full functionality on real systems with systemd.

debian/apt-ostree.postinst

@@ -28,18 +28,43 @@ setup_completions() {
     fi
 }
 
-# Function to check if systemd is available
+# Function to check if systemd is available and running
 check_systemd() {
+    # Check if systemctl command exists
     if ! command -v systemctl >/dev/null 2>&1; then
         log "Warning: systemd not available, skipping service setup"
         return 1
     fi
+    
+    # Check if we're in a container environment
+    if [ -f /.dockerenv ] || [ -n "${container:-}" ] || [ -f /run/.containerenv ] || \
+       ([ -f /proc/1/cgroup ] && grep -q docker /proc/1/cgroup 2>/dev/null); then
+        log "Warning: Running in container environment, skipping systemd service setup"
+        return 1
+    fi
+    
+    # Check if systemd is actually running as PID 1
+    if ! ps -p 1 -o comm= | grep -q systemd; then
+        log "Warning: systemd not running as PID 1, skipping service setup"
+        return 1
+    fi
+    
+    # Check if systemd D-Bus is available
+    if ! systemctl is-system-running >/dev/null 2>&1; then
+        log "Warning: systemd not running, skipping service setup"
+        return 1
+    fi
+    
     return 0
 }
 
 # Function to enable and start the service
 setup_service() {
     if ! check_systemd; then
+        log "Skipping systemd service configuration"
+        log "To configure services manually on a real system, run:"
+        log "  systemctl enable apt-ostreed.service"
+        log "  systemctl start apt-ostreed.service"
         return 0
     fi