fix(helpdesk): fix card coloring, dialog structure, search alignment

- Remove role=button from cards (caused Core button styling). Keep
  tabindex + keydown for keyboard access.
- Restructure dialog to Core pattern: dialog > article.app-dialog-lg
  > header > .close (uses Core close icon and positioning).
- Stack search input below segment control, left-aligned, full width
  up to 20rem.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

modules/helpdesk/web/css/helpdesk.css

@@ -523,15 +523,14 @@
   /* --- Risk Radar --- */
   .helpdesk-risk-radar-toolbar {
     display: flex;
-    align-items: center;
-    gap: calc(var(--app-spacing) * 0.75);
-    flex-wrap: wrap;
+    flex-direction: column;
+    align-items: flex-start;
+    gap: calc(var(--app-spacing) * 0.5);
     margin-bottom: calc(var(--app-spacing) * 0.75);
   }
 
   .helpdesk-risk-radar-search {
-    flex: 1;
-    min-width: 12rem;
+    width: 100%;
     max-width: 20rem;
   }