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/app/media_service.go

@@ -14,6 +14,7 @@ import (
 	"go.uber.org/zap"
 
 	"github.com/geo-platform/tenant-api/internal/shared/auth"
+	sharedcache "github.com/geo-platform/tenant-api/internal/shared/cache"
 	"github.com/geo-platform/tenant-api/internal/shared/response"
 )
 
@@ -22,12 +23,18 @@ const minBrowserExtensionVersion = "0.1.0"
 type MediaService struct {
 	pool   *pgxpool.Pool
 	logger *zap.Logger
+	cache  sharedcache.Cache
 }
 
 func NewMediaService(pool *pgxpool.Pool, logger *zap.Logger) *MediaService {
 	return &MediaService{pool: pool, logger: logger}
 }
 
+func (s *MediaService) WithCache(c sharedcache.Cache) *MediaService {
+	s.cache = c
+	return s
+}
+
 type MediaPlatformResponse struct {
 	ID          int64   `json:"id"`
 	PlatformID  string  `json:"platform_id"`
@@ -543,6 +550,7 @@ func (s *MediaService) CreatePublishBatch(ctx context.Context, articleID int64,
 	if err := tx.Commit(ctx); err != nil {
 		return nil, response.ErrInternal(50042, "publish_batch_commit_failed", "failed to commit publish batch")
 	}
+	invalidateArticleCaches(ctx, s.cache, actor.TenantID, &articleID)
 
 	return &CreatePublishBatchResponse{
 		PublishBatchID: publishBatchID,
@@ -829,6 +837,7 @@ func (s *MediaService) HandlePublishCallback(ctx context.Context, req PluginPubl
 	if err := tx.Commit(ctx); err != nil {
 		return nil, response.ErrInternal(50056, "publish_callback_commit_failed", "failed to commit publish callback")
 	}
+	invalidateArticleCaches(ctx, s.cache, session.TenantID, &articleID)
 
 	return &PluginPublishCallbackResponse{
 		PublishRecordID: req.PublishRecordID,