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/Domain/ClipSubmission.cs

@@ -0,0 +1,16 @@
+namespace Backend.Domain;
+
+public sealed class ClipSubmission
+{
+    public int Id { get; set; }
+    public int SeasonId { get; set; }
+    public int? CategoryId { get; set; }
+    public string SubmittedByTwitchId { get; set; } = string.Empty;
+    public string ClipUrl { get; set; } = string.Empty;
+    public string Title { get; set; } = string.Empty;
+    public string Creator { get; set; } = string.Empty;
+    public string Platform { get; set; } = string.Empty;
+    public string Status { get; set; } = "pending";
+    public string CreatedFromIp { get; set; } = string.Empty;
+    public DateTimeOffset CreatedAt { get; set; }
+}