fix: NUT template preview + tracking config event checkboxes

- Add NUT variables to _SAMPLE_CONTEXT (fixes ups_name undefined in preview)
- Add NUT event tracking checkboxes to tracking config form
- Add NUT event i18n keys (EN + RU)

packages/server/src/notify_bridge_server/services/sample_context.py

@@ -166,6 +166,19 @@ _SAMPLE_CONTEXT = {
     "attachment_id": "att-1",
     "label_name": "bug",
     "label_color": "berry-red",
+    # NUT (UPS) variables (for nut provider templates)
+    "ups_name": "kiper",
+    "ups_model": "Smart-UPS 1500",
+    "ups_manufacturer": "APC",
+    "battery_charge": 95,
+    "battery_runtime": "1:23:45",
+    "battery_runtime_seconds": 5025,
+    "ups_load": 42,
+    "ups_status": "OL",
+    "input_voltage": "230.0",
+    "output_voltage": "230.0",
+    "event_description": "UPS switched to battery power",
+    "previous_status": "OL",
     # Scheduler variables (for scheduler provider templates)
     "schedule_name": "Daily Reminder",
     "fire_count": 42,