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/Endpoints/AdminSeasonDetailEndpoints.cs

@@ -26,7 +26,13 @@ public static partial class AdminSeasonManagementEndpoints
                 item.CategoryId,
                 item.DisplayName,
                 item.ChannelSlug,
-                item.Platform))
+                item.Platform,
+                item.AcceptanceStatus,
+                item.AcceptanceNote,
+                item.ClipCompilationUrl,
+                item.ClipCompilationTitle,
+                item.ClipCompilationPlatform,
+                item.ClipEmbedStatus))
             .ToArrayAsync();
 
         var candidateCounts = candidates