refactor(plugin): rename detection_interval_seconds → detection_interval_minutes (#9366)

Minutes is the natural granularity for detection cadence — every
production handler already set the seconds field to a 60-multiple
(17*60, 30*60, 3600, 24*60*60). Switching to minutes drops the *60
arithmetic and matches the unit conventions used elsewhere in the
plugin worker forms.

- Proto: AdminRuntimeDefaults + AdminRuntimeConfig.detection_interval_*
  field renamed.
- Helpers: durationFromMinutes / minutesFromDuration alongside the
  existing seconds variants in plugin_scheduler.go.
- Handlers: vacuum, ec_balance, balance, erasure_coding, iceberg,
  admin_script, s3_lifecycle now declare DetectionIntervalMinutes.
- Admin: scheduler_status + types + UI templ + plugin_api.go pass
  through the new field; UI label and table cells switch to "min".

weed/admin/plugin/scheduler_status_test.go

@@ -90,7 +90,7 @@ func TestGetLaneSchedulerStatusShowsActiveConcurrentLaneWork(t *testing.T) {
 		JobType: jobType,
 		AdminRuntime: &plugin_pb.AdminRuntimeConfig{
 			Enabled:                  true,
-			DetectionIntervalSeconds: 30,
+			DetectionIntervalMinutes: 30,
 			DetectionTimeoutSeconds:  15,
 		},
 	})