feat(cache,worker): overhaul cache layer and add generation task lease recovery

- shared/cache: add Options/L1/async/metrics/prefix decorators, multi-key ops, Redis pool tuning, and JSON readthrough metrics
- worker-generate: claim tasks via DB lease + heartbeat, requeue stale queued tasks, expire dead leases with refund/cache invalidation
- tenant: version article cache keys so worker recovery invalidations propagate cleanly
- shared/config: expand Redis (pool/timeouts/TLS) and Generation (lease/recovery) configs with defaults

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

server/internal/tenant/app/generation_task_runtime.go

@@ -52,6 +52,9 @@ func HandleClaimedGenerationTaskFailure(
 	defer cancel()
 
 	errMsg := formatGenerationFailure("task_load", taskErr)
+	if taskErr != nil && strings.Contains(taskErr.Error(), "[worker_recovery]") {
+		errMsg = strings.TrimSpace(taskErr.Error())
+	}
 	now := time.Now()
 
 	auditRepo := repository.NewAuditRepository(pool)