refactor(httpapi): readiness ping via store backend

ARCH-09: Ping на store.Backend; readiness без прямого pgxpool.Ping в handler.
Co-authored-by: Cursor <cursoragent@cursor.com>

internal/httpapi/routes.go

@@ -84,12 +84,15 @@ func (s *Server) handleReady(w http.ResponseWriter, r *http.Request) {
 	checks := map[string]string{"store": "ok", "jobs": "memory"}
 	ctx, cancel := context.WithTimeout(r.Context(), 2*time.Second)
 	defer cancel()
-	if s.pgPool != nil {
-		if err := s.pgPool.Ping(ctx); err != nil {
+	if err := s.store.Ping(ctx); err != nil {
+		checks["store"] = "unavailable"
+		if s.pgPool != nil {
 			checks["postgres"] = "unavailable"
-			writeJSON(w, http.StatusServiceUnavailable, map[string]any{"status": "not_ready", "checks": checks})
-			return
 		}
+		writeJSON(w, http.StatusServiceUnavailable, map[string]any{"status": "not_ready", "checks": checks})
+		return
+	}
+	if s.pgPool != nil {
 		checks["postgres"] = "ok"
 	} else {
 		checks["store_backend"] = "memory"