feat(monitoring): decouple AI platforms from media_platforms and expand catalog to 6

Add ai_platforms table + shared catalog (yuanbao/kimi/wenxin/deepseek/doubao/qwen),
drop FKs from platform_accounts and desktop_tasks to media_platforms, and wire
target_account_id + platform into DesktopTaskEvent so the desktop runtime no
longer has to infer them from local state. Desktop client gains generic AI page
detection for binding, drops stale-business-date monitor tasks at the edge, and
refactors AccountsView/AiPlatformsView around the shared catalog. Admin tracking
view surfaces per-platform sampling status cards.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

server/internal/tenant/app/desktop_task_service.go

@@ -726,14 +726,16 @@ func (s *DesktopTaskService) publishTaskEvent(ctx context.Context, task *reposit
 	}
 
 	err := publishDesktopTaskEvent(ctx, s.messaging, DesktopTaskEvent{
-		Type:           eventType,
-		TaskID:         task.DesktopID.String(),
-		JobID:          task.JobID.String(),
-		WorkspaceID:    task.WorkspaceID,
-		TargetClientID: task.TargetClientID.String(),
-		Status:         task.Status,
-		Kind:           task.Kind,
-		UpdatedAt:      task.UpdatedAt,
+		Type:            eventType,
+		TaskID:          task.DesktopID.String(),
+		JobID:           task.JobID.String(),
+		WorkspaceID:     task.WorkspaceID,
+		TargetAccountID: task.TargetAccountID.String(),
+		TargetClientID:  task.TargetClientID.String(),
+		Platform:        task.Platform,
+		Status:          task.Status,
+		Kind:            task.Kind,
+		UpdatedAt:       task.UpdatedAt,
 	})
 	if err != nil {
 		s.logWarn("desktop task event publish failed", err, zap.String("task_id", task.DesktopID.String()), zap.String("event_type", eventType))