feat(workspace): replace supported platform count with bound media account count

The "platforms" stat tile was a constant (5) that never reflected what the
tenant actually had set up. Drop SupportedPlatformCount from the workspace
overview API/domain/shared-types and have admin-web compute a bound media
account count from the desktop accounts list, filtered through a new
isMediaPublishAccount helper that excludes deleted rows and AI-only
platforms (yuanbao/kimi/wenxin/deepseek/doubao/qwen).

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

server/internal/tenant/app/workspace_service.go

@@ -17,13 +17,12 @@ import (
 )
 
 type WorkspaceService struct {
-	repo                   repository.WorkspaceRepository
-	templates              repository.TemplateRepository
-	quota                  repository.QuotaRepository
-	aiPointUsage           repository.AIPointUsageRepository
-	supportedPlatformCount int
-	cache                  sharedcache.Cache
-	cacheGroup             singleflight.Group
+	repo         repository.WorkspaceRepository
+	templates    repository.TemplateRepository
+	quota        repository.QuotaRepository
+	aiPointUsage repository.AIPointUsageRepository
+	cache        sharedcache.Cache
+	cacheGroup   singleflight.Group
 }
 
 func NewWorkspaceService(
@@ -33,11 +32,10 @@ func NewWorkspaceService(
 	aiPointUsage repository.AIPointUsageRepository,
 ) *WorkspaceService {
 	return &WorkspaceService{
-		repo:                   repo,
-		templates:              templates,
-		quota:                  quota,
-		aiPointUsage:           aiPointUsage,
-		supportedPlatformCount: 5,
+		repo:         repo,
+		templates:    templates,
+		quota:        quota,
+		aiPointUsage: aiPointUsage,
 	}
 }
 
@@ -61,12 +59,10 @@ func (s *WorkspaceService) Overview(ctx context.Context) (*domain.WorkspaceOverv
 		if err != nil {
 			return nil, response.ErrInternal(50010, "query_failed", "failed to count brands")
 		}
-
 		return &domain.WorkspaceOverview{
-			ArticleCount:           articleCount,
-			PublishedCount:         publishedCount,
-			BrandCount:             brandCount,
-			SupportedPlatformCount: s.supportedPlatformCount,
+			ArticleCount:   articleCount,
+			PublishedCount: publishedCount,
+			BrandCount:     brandCount,
 		}, nil
 	})
 }

server/internal/tenant/domain/workspace.go

@@ -6,7 +6,6 @@ type WorkspaceOverview struct {
 	ArticleCount           int64 `json:"article_count"`
 	PublishedCount         int64 `json:"published_count"`
 	BrandCount             int64 `json:"brand_count"`
-	SupportedPlatformCount int   `json:"supported_platform_count"`
 }
 
 type RecentArticle struct {