Align backend with frontend, make clips end-to-end, polish admin

Backend
- Add ClipSubmission entity + table (runtime bootstrapper) and
  POST /api/public/clips (server-derives platform from the link)
- Surface clip submissions in the admin season detail
- Add DELETE candidate/category/clip endpoints with audit entries

Frontend
- Clips admin: real moderation view (list, open link, delete) instead
  of placeholder; wired clipSubmissions through types/api/store
- Categories admin: add delete with confirm modal (matches Candidates)
- Voting ranking bar uses the unified purple gradient
- Fix ASCII transliterations to proper German umlauts across admin
- Remove orphan AdminView 2.vue

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Backend/Contracts/AdminContracts.cs

@@ -67,6 +67,17 @@ public sealed record AdminNominationReviewItemDto(
     string CandidateText,
     DateTimeOffset CreatedAt);
 
+public sealed record AdminClipSubmissionItemDto(
+    int Id,
+    int? CategoryId,
+    string SubmittedByTwitchId,
+    string ClipUrl,
+    string Title,
+    string Creator,
+    string Platform,
+    string Status,
+    DateTimeOffset CreatedAt);
+
 public sealed record AdminSeasonDetailResponse(
     int Id,
     int Year,
@@ -75,7 +86,8 @@ public sealed record AdminSeasonDetailResponse(
     bool IsCurrent,
     IEnumerable<AdminCategoryItemDto> Categories,
     IEnumerable<AdminCandidateItemDto> Candidates,
-    IEnumerable<AdminNominationReviewItemDto> PendingNominations);
+    IEnumerable<AdminNominationReviewItemDto> PendingNominations,
+    IEnumerable<AdminClipSubmissionItemDto> ClipSubmissions);
 
 public sealed record UpdateSeasonRequest(
     string CurrentPhase,