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/Data/SeedData.cs

@@ -48,7 +48,17 @@ Keine Weitergabe zu Werbezwecken. Technische Dienstleister verarbeiten Daten aus
                 ContactContent = SeedCatalog.DefaultContactContent,
                 SponsorsUrl = "https://vtuber-star-awards.de/partner",
                 SponsorsContent = SeedCatalog.DefaultSponsorsContent,
+                ShowactsUrl = "https://vtuber-star-awards.de/showacts",
+                ShowactsContent = "Informationen zu Showact-Bewerbungen, Ablauf und Kontakt fuer die Award-Show.",
                 RiskRulesJson = RiskRuleSettings.Serialize(RiskRuleSettings.Defaults),
+                WorkflowRulesJson = WorkflowRuleSettings.Serialize(WorkflowRuleSettings.Defaults),
+                NominationLinkBlacklistJson = NominationLinkBlacklistSettings.Serialize(NominationLinkBlacklistSettings.Defaults),
+                ClipSubmissionsEnabled = false,
+                ClipReviewEnabled = true,
+                ClipSubmissionDisabledMessage = "Clip-Einreichungen sind aktuell geschlossen.",
+                ShowactApplicationsEnabled = false,
+                ShowactApplicationDisabledMessage = "Showact-Bewerbungen sind aktuell geschlossen.",
+                SponsorsVisible = true,
                 SocialLinksJson = JsonSerializer.Serialize(new[]
                 {
                     new { label = "Twitch", platform = "twitch", url = "https://twitch.tv/jayuhime", icon = "twitch", showOnHost = true, showOnCommunity = true },