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/AdminModerationContracts.cs

@@ -91,6 +91,14 @@ public sealed record ApproveNominationRequest(
 
 public sealed record RejectNominationRequest(string? ReviewNote);
 
+public sealed record AdminNominationLinkBlacklistEntryDto(string Url);
+
+public sealed record AdminNominationLinkBlacklistResponse(AdminNominationLinkBlacklistEntryDto[] Entries);
+
+public sealed record UpdateNominationLinkBlacklistRequest(string[] Urls);
+
+public sealed record AddNominationLinkBlacklistEntryRequest(string Url);
+
 public sealed record UpdateClipStatusRequest(
     string Status,
     string? ReviewNote);
@@ -116,3 +124,15 @@ public sealed record AdminRiskRuleDto(
 public sealed record AdminRiskRulesResponse(AdminRiskRuleDto[] Rules);
 
 public sealed record UpdateRiskRulesRequest(AdminRiskRuleDto[] Rules);
+
+public sealed record AdminWorkflowRuleDto(
+    string Key,
+    string Label,
+    bool Enabled,
+    int Limit,
+    string Mode,
+    string Description);
+
+public sealed record AdminWorkflowRulesResponse(AdminWorkflowRuleDto[] Rules);
+
+public sealed record UpdateWorkflowRulesRequest(AdminWorkflowRuleDto[] Rules);