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>

Backend/Contracts/PublicOverviewContracts.cs

@@ -50,6 +50,8 @@ public sealed record PublicSiteContentDto(
     string HostDisplayName,
     string HostTagline,
     string NewsletterUrl,
+    string ShareXUrl,
+    string ShareDiscordUrl,
     string PrivacyEmail,
     string PrivacyPolicyContent,
     IEnumerable<PublicSocialLinkDto> SocialLinks,
@@ -66,8 +68,11 @@ public sealed record PublicFeatureFlagsDto(
     bool ClipReviewEnabled,
     string ClipSubmissionDisabledMessage,
     bool ShowactApplicationsEnabled,
+    DateOnly? ShowactApplicationStartsAt,
+    DateOnly? ShowactApplicationEndsAt,
     string ShowactApplicationDisabledMessage,
-    bool SponsorsVisible);
+    bool SponsorsVisible,
+    string ShowactFormSchemaJson);
 
 public sealed record OverviewResponse(
     int SeasonId,