old_contents: from django.contrib import admin
  from blinky.core.models import System, WorkerType, WorkerInstance, HeartBeat
  
  
  @admin.register(HeartBeat)
  class HeartBeatAdmin(admin.ModelAdmin):
      list_filter = ('worker_instance', 'system', 'timestamp')
      list_display = ('worker_instance', 'timestamp', 'created_at')
  
  
  @admin.register(WorkerType)
  class WorkerAdmin(admin.ModelAdmin):
      list_filter = ('system',)
      list_display = (
          'system', 'worker_name', 'worker_friendly_name', 'created_at',
          'status', 'capacity', 'last_seen_at')
  
      def last_seen_at(self, worker_type):
          last_instance = worker_type.last_seen_instance()
          if last_instance:
              return last_instance.last_seen_at()
  
  
  @admin.register(WorkerInstance)
  class WorkerInstanceAdmin(admin.ModelAdmin):
      list_filter = ('worker_type',)
      list_display = ('hostname', 'pid', 'worker_type',
                      'is_online', 'last_seen_at')
  
  
  @admin.register(System)
  class SystemAdmin(admin.ModelAdmin):
      list_filter = ('created_at',)
      list_display = ('system_id', 'created_at', 'is_online')
  
new_contents: from django.contrib import admin
  from blinky.core.models import System, WorkerType, WorkerInstance, HeartBeat
  
  
  @admin.register(HeartBeat)
  class HeartBeatAdmin(admin.ModelAdmin):
      list_filter = ('worker_instance', 'system', 'timestamp')
      list_display = ('worker_instance', 'timestamp', 'created_at')
  
  
  @admin.register(WorkerType)
  class WorkerTypeAdmin(admin.ModelAdmin):
      list_filter = ('system',)
      list_display = (
          'system', 'worker_name', 'worker_friendly_name', 'created_at',
          'status', 'last_seen_at')
  
      def last_seen_at(self, worker_type):
          last_instance = worker_type.last_seen_instance()
          if last_instance:
              return last_instance.last_seen_at()
  
  
  @admin.register(WorkerInstance)
  class WorkerInstanceAdmin(admin.ModelAdmin):
      list_filter = ('worker_type',)
      list_display = ('hostname', 'pid', 'worker_type',
                      'is_online', 'last_seen_at')
  
  
  @admin.register(System)
  class SystemAdmin(admin.ModelAdmin):
      list_filter = ('created_at',)
      list_display = ('system_id', 'created_at', 'is_online')
  
subject: remove capacity column from admin