fix: address a11y code review findings

Bugs fixed:
- Space key was hijacked in tag input when a suggestion was
  highlighted, preventing users from typing spaces. Removed
  Space as a selection key (Enter is sufficient per combobox
  pattern).
- ArrowUp was clamped to index 0, making it impossible to
  deselect all suggestions and return to free typing. Now
  allows arrowing back to -1 which clears aria-activedescendant.

Cleanup:
- Remove dead inline onkeydown handlers from tag suggestion
  <li> elements (tabindex="-1" means they never receive focus,
  so the handlers never fire; the global keydown listener in
  app.js handles keyboard navigation).
- Add outline to aria-selected="true" state for visual parity
  with hover (keyboard users now see the same indicator).
- Announce "Ingen forslag" in live region when suggestions are
  empty (screen readers previously got silence).
- Add responsive table wrapper to admin tags and admin requests
  tables (was only on admin users).

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

web/templates/pages/admin_requests.html

@@ -7,6 +7,7 @@
 
 {{with .Data}}
     {{if .Requests}}
+        <div class="table-responsive" role="region" aria-label="Forespørsler" tabindex="0">
         <table role="grid">
             <thead>
                 <tr>
@@ -37,6 +38,7 @@
                 {{end}}
             </tbody>
         </table>
+        </div>
     {{else}}
         <p>Ingen ventende forespørsler.</p>
     {{end}}

web/templates/pages/admin_tags.html

@@ -7,6 +7,7 @@
 
 {{with .Data}}
     {{if .Tags}}
+        <div class="table-responsive" role="region" aria-label="Merkelapp-tabell" tabindex="0">
         <table role="grid">
             <thead>
                 <tr>
@@ -35,6 +36,7 @@
                 {{end}}
             </tbody>
         </table>
+        </div>
     {{else}}
         <p>Ingen merkelapper ennå.</p>
     {{end}}