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/ExtrasContracts.cs

@@ -36,16 +36,18 @@ public sealed record ShowactApplicationDto(
     string Status,
     string? ReviewNote,
     DateTimeOffset CreatedAt,
-    DateTimeOffset? ReviewedAt);
+    DateTimeOffset? ReviewedAt,
+    string FieldResponsesJson);
 
 public sealed record CreateShowactApplicationRequest(
-    string ArtistName,
-    string ContactEmail,
-    string ContactDiscord,
-    string PlatformUrl,
-    string PerformanceType,
-    string Description,
-    string TechnicalNotes,
-    string ReferenceUrl);
+    string? ArtistName = null,
+    string? ContactEmail = null,
+    string? ContactDiscord = null,
+    string? PlatformUrl = null,
+    string? PerformanceType = null,
+    string? Description = null,
+    string? TechnicalNotes = null,
+    string? ReferenceUrl = null,
+    string? FieldResponsesJson = null);
 
 public sealed record UpdateShowactStatusRequest(string Status, string? ReviewNote);