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/Contracts/ExtrasContracts.cs

@@ -0,0 +1,51 @@
+namespace Backend.Contracts;
+
+public sealed record SponsorDto(
+    int Id,
+    int SeasonId,
+    string Name,
+    string WebsiteUrl,
+    string LogoUrl,
+    string Description,
+    string Tier,
+    int SortOrder,
+    bool IsVisible);
+
+public sealed record PublicSponsorsResponse(int Year, SponsorDto[] Items);
+
+public sealed record UpsertSponsorRequest(
+    string Name,
+    string WebsiteUrl,
+    string LogoUrl,
+    string Description,
+    string Tier,
+    int SortOrder,
+    bool IsVisible);
+
+public sealed record ShowactApplicationDto(
+    int Id,
+    int SeasonId,
+    string ArtistName,
+    string ContactEmail,
+    string ContactDiscord,
+    string PlatformUrl,
+    string PerformanceType,
+    string Description,
+    string TechnicalNotes,
+    string ReferenceUrl,
+    string Status,
+    string? ReviewNote,
+    DateTimeOffset CreatedAt,
+    DateTimeOffset? ReviewedAt);
+
+public sealed record CreateShowactApplicationRequest(
+    string ArtistName,
+    string ContactEmail,
+    string ContactDiscord,
+    string PlatformUrl,
+    string PerformanceType,
+    string Description,
+    string TechnicalNotes,
+    string ReferenceUrl);
+
+public sealed record UpdateShowactStatusRequest(string Status, string? ReviewNote);