Improve admin candidate modal UX and add clip menu visibility toggle

- Widen AdminCandidateEditorModal to size lg for better readability
- Rename "Clip-Compilation" section to "Clip / Compilation", update copy to reflect single clips too, drop upload hint and Clip-Plattform field, rename label to "Link"
- Fix NativeSelect dropdown clipping inside overflow-y-auto modals by teleporting the menu to body with fixed positioning, flip-up logic, and dynamic maxHeight capped to viewport
- Add ClipAdminMenuVisible setting (backend domain, contracts, endpoint, migration) with matching frontend types, defaults, form wiring, and toggle in the Clip-Workflow modal — hides the Clips nav item from the admin sidebar when disabled

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

Backend/Domain/ShowactApplication.cs

@@ -0,0 +1,23 @@
+namespace Backend.Domain;
+
+public sealed class ShowactApplication
+{
+    public int Id { get; set; }
+    public int SeasonId { get; set; }
+    public Season Season { get; set; } = null!;
+    public string ArtistName { get; set; } = string.Empty;
+    public string ContactEmail { get; set; } = string.Empty;
+    public string ContactDiscord { get; set; } = string.Empty;
+    public string PlatformUrl { get; set; } = string.Empty;
+    public string PerformanceType { get; set; } = string.Empty;
+    public string Description { get; set; } = string.Empty;
+    public string TechnicalNotes { get; set; } = string.Empty;
+    public string ReferenceUrl { get; set; } = string.Empty;
+    public string Status { get; set; } = "pending";
+    public string? ReviewNote { get; set; }
+    public string? ReviewedByTwitchId { get; set; }
+    public string CreatedFromIp { get; set; } = string.Empty;
+    public string UserAgent { get; set; } = string.Empty;
+    public DateTimeOffset CreatedAt { get; set; } = DateTimeOffset.UtcNow;
+    public DateTimeOffset? ReviewedAt { get; set; }
+}