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/Domain/StreamerIdentity.cs

@@ -0,0 +1,14 @@
+namespace Backend.Domain;
+
+public sealed class StreamerIdentity
+{
+    public int Id { get; set; }
+    public string Platform { get; set; } = string.Empty;
+    public string Login { get; set; } = string.Empty;
+    public string NormalizedKey { get; set; } = string.Empty;
+    public string DisplayName { get; set; } = string.Empty;
+    public string? ProfileUrl { get; set; }
+    public DateTimeOffset? LastResolvedAt { get; set; }
+    public ICollection<Nomination> Nominations { get; set; } = [];
+    public ICollection<Candidate> Candidates { get; set; } = [];
+}