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/PublicContracts.cs

@@ -77,3 +77,11 @@ public sealed record CreateVoteRequest(
     int SeasonId,
     string TwitchUserId,
     VoteEntryRequest[] Entries);
+
+public sealed record CreateClipRequest(
+    int Year,
+    int? CategoryId,
+    string TwitchUserId,
+    string ClipUrl,
+    string Title,
+    string Creator);