fix: reduce log noise and guard against non-dict SNMP devices

- SNMP scheduler: skip non-dict entries in devices list (prevents AttributeError)
- UPS scheduler: downgrade NutError from exception to warning (expected when NUT not running)
- UniFi scheduler: downgrade login/poll failures from exception to warning (expected when controller unreachable)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

ups/scheduler.py

@@ -53,8 +53,8 @@ async def _do_poll(app: "Quart") -> None:
 
     try:
         raw_vars = await client.get_vars(cfg.get("ups_name", "ups"))
-    except NutError:
-        logger.exception("UPS poll failed")
+    except NutError as exc:
+        logger.warning("UPS poll failed: %s", exc)
         return
 
     parsed = parse_status(raw_vars)