Switch to uptime-kuma-api-v2 for Kuma v2 support

The original uptime-kuma-api library doesn't support Uptime Kuma v2's
required conditions field. The v2 fork has the same API but properly
supports the newer schema.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

backend/services/kuma_client.py

@@ -203,7 +203,6 @@ class UptimeKumaClient:
                 "interval": monitor.interval,
                 "maxretries": monitor.retries,
                 "retryInterval": monitor.retry_interval,
-                "conditions": [],  # Required for Uptime Kuma v2
             }
 
             # Add type-specific fields