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/generation_task_runtime.go

@@ -6,6 +6,7 @@ import (
 	"strings"
 	"time"
 
+	"github.com/jackc/pgx/v5"
 	"github.com/jackc/pgx/v5/pgxpool"
 
 	"github.com/geo-platform/tenant-api/internal/shared/llm"
@@ -22,6 +23,23 @@ type ClaimedGenerationTask struct {
 	InputParams        map[string]interface{}
 }
 
+const generationCleanupTimeout = 30 * time.Second
+
+func newGenerationCleanupContext() (context.Context, context.CancelFunc) {
+	return context.WithTimeout(context.Background(), generationCleanupTimeout)
+}
+
+func rollbackGenerationTx(tx pgx.Tx) {
+	if tx == nil {
+		return
+	}
+
+	ctx, cancel := newGenerationCleanupContext()
+	defer cancel()
+
+	_ = tx.Rollback(ctx)
+}
+
 func HandleClaimedGenerationTaskFailure(
 	ctx context.Context,
 	pool *pgxpool.Pool,
@@ -30,6 +48,9 @@ func HandleClaimedGenerationTaskFailure(
 	task ClaimedGenerationTask,
 	taskErr error,
 ) error {
+	cleanupCtx, cancel := newGenerationCleanupContext()
+	defer cancel()
+
 	errMsg := formatGenerationFailure("task_load", taskErr)
 	now := time.Now()
 
@@ -37,7 +58,7 @@ func HandleClaimedGenerationTaskFailure(
 	articleRepo := repository.NewArticleRepository(pool)
 	quotaRepo := repository.NewQuotaRepository(pool)
 
-	_ = auditRepo.UpdateGenerationTaskStatus(ctx, repository.GenerationTaskStatusInput{
+	_ = auditRepo.UpdateGenerationTaskStatus(cleanupCtx, repository.GenerationTaskStatusInput{
 		ID:           task.ID,
 		TenantID:     task.TenantID,
 		Status:       "failed",
@@ -45,16 +66,16 @@ func HandleClaimedGenerationTaskFailure(
 		CompletedAt:  &now,
 	})
 	if task.ArticleID > 0 {
-		_ = articleRepo.UpdateArticleGenerateStatus(ctx, task.ArticleID, task.TenantID, "failed")
+		_ = articleRepo.UpdateArticleGenerateStatus(cleanupCtx, task.ArticleID, task.TenantID, "failed")
 	}
 
 	if task.QuotaReservationID > 0 {
-		balance, balanceErr := quotaRepo.GetCurrentBalance(ctx, task.TenantID, "article_generation")
+		balance, balanceErr := quotaRepo.GetCurrentBalance(cleanupCtx, task.TenantID, "article_generation")
 		if balanceErr == nil && task.OperatorID > 0 {
 			reason := "generation_refund"
 			referenceType := "generation_task"
 			taskReferenceID := task.ID
-			_, _ = quotaRepo.InsertQuotaLedger(ctx, repository.QuotaLedgerInput{
+			_, _ = quotaRepo.InsertQuotaLedger(cleanupCtx, repository.QuotaLedgerInput{
 				TenantID:      task.TenantID,
 				OperatorID:    task.OperatorID,
 				QuotaType:     "article_generation",
@@ -66,7 +87,16 @@ func HandleClaimedGenerationTaskFailure(
 			})
 		}
 
-		_ = quotaRepo.RefundReservation(ctx, task.QuotaReservationID, task.TenantID)
+		_ = quotaRepo.RefundReservation(cleanupCtx, task.QuotaReservationID, task.TenantID)
+	}
+
+	if task.ArticleID > 0 {
+		switch {
+		case templateService != nil && templateService.cache != nil:
+			invalidateArticleCaches(cleanupCtx, templateService.cache, task.TenantID, &task.ArticleID)
+		case promptRuleService != nil && promptRuleService.cache != nil:
+			invalidateArticleCaches(cleanupCtx, promptRuleService.cache, task.TenantID, &task.ArticleID)
+		}
 	}
 
 	title := resolveArticleTitle(task.InputParams, "")