Add viewer-range categories, nomination tracking, dynamic showact form, session timeout, share URLs, and workflow-per-season

Features:
- Category viewer ranges + subcategory templates (admin group modal, tree workspace)
- Nomination enrichment via TwitchTracker API (NominationEnrichmentService,
  TwitchTrackerViewerStatsProvider) with admin tracking rules editor
- Nomination group tracker: CategoryGroupName as primary identifier,
  CategoryId stays as nullable legacy field; StreamerIdentity table
- Dynamic showact application form builder (AdminShowactFormBuilder,
  ShowactApplicationSchedule)
- Session idle timeout setting (AdminSessionTimeoutCard)
- Share URLs for X and Discord (SiteSettings, public extras)
- Workflow rules now stored per season (falls back to global SiteSettings)
- New admin routes: settings/access, settings/workflows, tracking-rules
- New admin review workspace with subcategory tabs
- AdminCategoriesView rebuilt with group/subcategory modals

Migrations (all additive):
- AddShareUrls, AddShowactDynamicForm, AddCategoryViewerRanges,
  AddSessionIdleTimeoutSettings, AddSeasonSubcategoryTemplates,
  AddNominationGroupTrackerIdentity, AddShowactApplicationSchedule,
  AddSeasonWorkflowRulesJson

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/views/admin/AdminClipsView.vue

@@ -199,16 +199,21 @@ watchAdminToast(adminMessage, adminError)
             </div>
           </div>
           <div class="min-w-0">
-            <div v-if="clipEmbeds[clip.id]" class="overflow-hidden rounded-2xl border border-violet-100 bg-slate-950 shadow-sm">
-              <iframe
-                class="aspect-video w-full"
-                :src="clipEmbeds[clip.id]?.src"
-                :title="clip.title || `${clip.platform} Clip ${clip.id}`"
-                loading="lazy"
-                allow="accelerometer; autoplay; clipboard-write; encrypted-media; fullscreen; picture-in-picture; web-share"
-                allowfullscreen
-                referrerpolicy="strict-origin-when-cross-origin"
-              />
+            <div v-if="clipEmbeds[clip.id]">
+              <div class="overflow-hidden rounded-2xl border border-violet-100 bg-slate-950 shadow-sm">
+                <iframe
+                  class="aspect-video w-full"
+                  :src="clipEmbeds[clip.id]?.src"
+                  :title="clip.title || `${clip.platform} Clip ${clip.id}`"
+                  loading="lazy"
+                  allow="accelerometer; autoplay; clipboard-write; encrypted-media; fullscreen; picture-in-picture; web-share"
+                  allowfullscreen
+                  referrerpolicy="strict-origin-when-cross-origin"
+                />
+              </div>
+              <p class="mt-2 text-xs text-slate-400">
+                Falls der Clip nicht lädt oder nicht mehr verfügbar ist, öffne ihn direkt über den Clip-Link.
+              </p>
             </div>
             <div v-else class="rounded-2xl border border-dashed border-amber-200 bg-amber-50 px-4 py-5 text-sm font-medium leading-6 text-amber-800">
               Dieser Clip kann nicht eingebettet werden. Öffne ihn über den Clip-Link zur manuellen Prüfung.