fix: disk_usage_check.sh handles inode '-' (vfat/efi), checkdefaults sets target_id

- disk_usage_check.sh: sed 's/-/0/' for filesystems without inodes
- checkdefaults.Ensure: includes target_id in check_defs INSERT so
  signals get proper target slug instead of null

internal/checkdefaults/defaults.go

@@ -196,9 +196,9 @@ func Ensure(ctx context.Context, tx pgx.Tx, entityID uuid.UUID, slug, entityType
 		configJSON, _ := json.Marshal(configMap)
 
 		_, _ = tx.Exec(ctx,
-			`INSERT INTO check_defs (entity_id, kind, config, interval_s, timeout_s, enabled)
-			 VALUES ($1, $2, $3, $4, 30, true)
+			`INSERT INTO check_defs (entity_id, target_id, kind, config, interval_s, timeout_s, enabled)
+			 VALUES ($1, $2, $3, $4, $5, 30, true)
 			 ON CONFLICT (entity_id) DO NOTHING`,
-			checkID, def.Kind, configJSON, DefaultInterval(def.Kind))
+			checkID, entityID, def.Kind, configJSON, DefaultInterval(def.Kind))
 	}
 }