refactor(webui): relocate dashboard into features/dashboard/

Move dashboard.js + dashboard.css into the feature folder (kept eager-linked
from the new paths in index.html — dashboard.js stays eager because
system-loader calls its bare globals at boot). No reference sites outside
index.html (the feature's index.js uses globals, not the controller path).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Signed-off-by: librelad <librelad@digitalangels.vip>

containers/libreportal/frontend/index.html

@@ -34,7 +34,7 @@
   <link rel="stylesheet" href="/css/forms.css">
   <link rel="stylesheet" href="/css/config.css">
   <link rel="stylesheet" href="/css/service-buttons.css">
-  <link rel="stylesheet" href="/css/dashboard.css">
+  <link rel="stylesheet" href="/features/dashboard/dashboard.css">
   <link rel="stylesheet" href="/css/tasks.css">
   <link rel="stylesheet" href="/css/update-notifier.css">
   <script>
@@ -97,7 +97,7 @@
   <script src="/js/utils/dismissible.js"></script>
   <script src="/js/components/eo-modal.js"></script>
   <script src="/js/components/task/task-refresh-coordinator.js"></script>
-  <script src="/js/components/dashboard.js"></script>
+  <script src="/features/dashboard/dashboard.js"></script>
   <script src="/js/system/system-loader.js"></script>
   <script src="/js/system/loading-ui.js"></script>
   <script src="/js/system/setup-detector.js"></script>