printedparts stage 12: admin settings page + settings-rail card

PrintedPartsSettings edits the four plugin settings (code prefix,
default threshold, kiosk badge policy, alert recipients) through the
core settings API; the route rides the plugin's router file and the
settings shell nests it into the rail; get_settings_cards contributes
the catalog card while the plugin is enabled.

plugins/printedparts/plugin.py

@@ -62,6 +62,19 @@ class PrintedpartsPlugin(BasePlugin):
              'printedparts'),
         ]
 
+    def get_settings_cards(self) -> List[dict]:
+        return [
+            {
+                'group': '3D Printed Parts',
+                'to': '/settings/printedparts',
+                'icon': 'box',
+                'title': '3D Parts Settings',
+                'description': 'Item code prefix, default threshold, kiosk '
+                               'badge policy, low-stock alert recipients',
+                'position': 47,
+            },
+        ]
+
     def get_reports(self) -> List[dict]:
         return [
             {