Add PostGIS extension check to Reitti update_script

Automatically enable PostGIS extension on existing installations if missing.
Checks if extension is already enabled before attempting to create it.

Fixes existing Reitti installations that were created before PostGIS was
added to the initial setup (commit b6312b87d).

Users no longer need to manually run 'CREATE EXTENSION postgis;'

ct/reitti.sh

@@ -28,6 +28,15 @@ function update_script() {
     exit
   fi
 
+  # Enable PostGIS extension if not already enabled
+  if systemctl is-active --quiet postgresql; then
+    if ! sudo -u postgres psql -d reitti -tAc "SELECT 1 FROM pg_extension WHERE extname='postgis'" 2>/dev/null | grep -q 1; then
+      msg_info "Enabling PostGIS extension"
+      sudo -u postgres psql -d reitti -c "CREATE EXTENSION IF NOT EXISTS postgis;" &>/dev/null
+      msg_ok "Enabled PostGIS extension"
+    fi
+  fi
+
   if [ ! -d /var/cache/nginx/tiles ]; then
     msg_info "Installing Nginx Tile Cache"
     mkdir -p /var/cache/nginx/tiles