feat(cache): add read-through cache layer across all app services

Introduce a generic read-through caching infrastructure and wire it into
all major tenant app services to reduce database load on hot read paths.

Key changes:
- Add `DeletePrefix` to Cache interface with memory (prefix scan) and
  Redis (SCAN + DEL) implementations
- New `readthrough.go`: generic `LoadJSON` / `LoadJSONWithEmpty` helpers
  backed by singleflight to prevent cache stampedes; supports jittered TTL
- New `cache_support.go`: centralized cache key builders and invalidation
  helpers for all entities (workspace, brand, prompt rules, schedule tasks,
  articles)
- Wire optional cache into ArticleService, BrandService, WorkspaceService,
  PromptRuleService, ScheduleTaskService, TemplateService, MediaService,
  PromptGenerateService via `WithCache()` builder pattern
- ScheduleDispatchWorker invalidates schedule task cache after dispatching
- ArticleService gains a new `Detail` endpoint with empty-result caching
- Update cmd entrypoints and transport handlers to propagate cache

server/internal/tenant/transport/article_handler.go

@@ -42,7 +42,7 @@ func NewArticleHandler(a *bootstrap.App) *ArticleHandler {
 	)
 
 	return &ArticleHandler{
-		svc: app.NewArticleService(a.DB, a.AuditLogs, a.ObjectStorage),
+		svc: app.NewArticleService(a.DB, a.AuditLogs, a.ObjectStorage).WithCache(a.Cache),
 		selectionOptimize: app.NewArticleSelectionOptimizeService(
 			a.DB,
 			a.LLM,
@@ -56,7 +56,7 @@ func NewArticleHandler(a *bootstrap.App) *ArticleHandler {
 			a.GenerationStreams,
 			a.Config.Generation,
 			a.Config.LLM.MaxOutputTokens,
-		),
+		).WithCache(a.Cache),
 		streams:       a.GenerationStreams,
 		streamEnabled: a.Config.Generation.StreamEnabled,
 		assets:        NewAssetHandler(a),

server/internal/tenant/transport/brand_handler.go

@@ -15,7 +15,7 @@ type BrandHandler struct {
 }
 
 func NewBrandHandler(a *bootstrap.App) *BrandHandler {
-	return &BrandHandler{svc: app.NewBrandService(a.DB, a.MonitoringDB, a.AuditLogs)}
+	return &BrandHandler{svc: app.NewBrandService(a.DB, a.MonitoringDB, a.AuditLogs).WithCache(a.Cache)}
 }
 
 func (h *BrandHandler) List(c *gin.Context) {

server/internal/tenant/transport/media_handler.go

@@ -18,7 +18,7 @@ type MediaHandler struct {
 
 func NewMediaHandler(a *bootstrap.App) *MediaHandler {
 	return &MediaHandler{
-		svc:    app.NewMediaService(a.DB, a.Logger),
+		svc:    app.NewMediaService(a.DB, a.Logger).WithCache(a.Cache),
 		logger: a.Logger,
 	}
 }

server/internal/tenant/transport/prompt_rule_handler.go

@@ -15,7 +15,7 @@ type PromptRuleHandler struct {
 }
 
 func NewPromptRuleHandler(a *bootstrap.App) *PromptRuleHandler {
-	return &PromptRuleHandler{svc: app.NewPromptRuleService(a.DB, a.AuditLogs)}
+	return &PromptRuleHandler{svc: app.NewPromptRuleService(a.DB, a.AuditLogs).WithCache(a.Cache)}
 }
 
 // --- Groups ---

server/internal/tenant/transport/schedule_task_handler.go

@@ -16,7 +16,7 @@ type ScheduleTaskHandler struct {
 }
 
 func NewScheduleTaskHandler(a *bootstrap.App) *ScheduleTaskHandler {
-	return &ScheduleTaskHandler{svc: app.NewScheduleTaskService(a.DB, a.AuditLogs)}
+	return &ScheduleTaskHandler{svc: app.NewScheduleTaskService(a.DB, a.AuditLogs).WithCache(a.Cache)}
 }
 
 func (h *ScheduleTaskHandler) List(c *gin.Context) {

server/internal/tenant/transport/template_handler.go

@@ -42,7 +42,7 @@ func NewTemplateHandler(a *bootstrap.App) *TemplateHandler {
 			a.GenerationStreams,
 			a.Config.Generation,
 			a.Config.LLM.MaxOutputTokens,
-		),
+		).WithCache(a.Cache),
 	}
 }
 

server/internal/tenant/transport/workspace_handler.go

@@ -21,7 +21,7 @@ func NewWorkspaceHandler(a *bootstrap.App) *WorkspaceHandler {
 				repository.NewTemplateRepository(a.DB),
 				a.Cache,
 			),
-		),
+		).WithCache(a.Cache),
 	}
 }