SSR module: live progress bar for cache warming

The Cache warming row of the VITEC SSR module now shows a Bootstrap progress bar with a running counter instead of asking for a reload. New ajax route vitec_ssr_health (SsrController::healthJson) returns the node /__health JSON; ssr-warm-progress.js polls it every 2 s while a warm run is active and every 15 s otherwise (pauses in background tabs) and also refreshes the Cache: N pages / M MB line. The health fetch moved into SsrController::fetchHealth, shared by indexAction and the ajax route; its error text is English now. Verified live in the backend: bar, counter and cache line advance during a run.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

packages/vitec/Configuration/Backend/AjaxRoutes.php

@@ -33,4 +33,10 @@ return [
         'path' => '/vitec/ssr/purge-page',
         'target' => \Evomedien\Vitec\Controller\Backend\SsrController::class . '::purgePage',
     ],
+    // Live "Cache warming" progress bar in the VITEC SSR module
+    // (Resources/Public/Javascript/ssr-warm-progress.js polls it).
+    'vitec_ssr_health' => [
+        'path' => '/vitec/ssr/health',
+        'target' => \Evomedien\Vitec\Controller\Backend\SsrController::class . '::healthJson',
+    ],
 ];