fix: DatasetPreview dashboard links missing env_id

Dashboard links in DatasetPreview were constructed without env_id query
parameter, causing 'Отсутствует ID дашборда или окружения' error when
clicking through from dataset detail. Use ROUTES.dashboards.detail()
helper which correctly appends ?env_id= to the URL.

frontend/src/routes/datasets/DatasetPreview.svelte

@@ -10,6 +10,7 @@
 <!-- @UX_STATE Error -> Error banner with retry. -->
 <script lang="ts">
   import { t } from "$lib/i18n/index.svelte.js";
+  import { ROUTES } from "$lib/routes.js";
   import ColumnsTable from "./ColumnsTable.svelte";
   import MetricsTable from "./MetricsTable.svelte";
 
@@ -58,7 +59,7 @@
       {#if dataset.linked_dashboards?.length}
         <div class="flex gap-1.5 mt-2 flex-wrap">
           {#each dataset.linked_dashboards as dash}
-            <a href={`/dashboards/${dash.slug || dash.id}`} class="inline-block px-2 py-0.5 text-xs bg-primary-light text-primary rounded-full hover:bg-primary-light">
+            <a href={ROUTES.dashboards.detail(String(dash.slug || dash.id), envId)} class="inline-block px-2 py-0.5 text-xs bg-primary-light text-primary rounded-full hover:bg-primary-light">
               {dash.title}
             </a>
           {/each}