Add winner archive, host image upload and live demo data

Deliver the demo-ready feature set and seed data so the live site can be
presented end to end:

- Winner archive: ArchivedWinner domain, admin CRUD endpoints/view/manager
  and public archive surface, backed by AddArchivedWinners migration.
- Host presentation: host image upload and artist name on SiteSettings with
  public image endpoint and supporting migrations.
- Clip submissions: idempotent table-ensure migration plus current-season
  demo clips for review workflows.
- Demo seed data: sponsors, share links and 2025 archived winners, with a
  guarded RemoveDemoSeasons cleanup; all seeds guard against real data.
- EnsureRuntimeSchemaParity migration to align runtime schema defensively.
- Admin/home UI refinements; remove unused team role permissions modal and
  dead share-quick-links code.

All seed and schema migrations are idempotent (IF NOT EXISTS / ON CONFLICT)
and skip when real season data is present.

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

Backend/Endpoints/PublicHostImageEndpoints.cs

@@ -0,0 +1,35 @@
+using Backend.Data;
+using Microsoft.EntityFrameworkCore;
+
+namespace Backend.Endpoints;
+
+public static partial class PublicEndpoints
+{
+    private static async Task<IResult> GetHostImage(AwardsDbContext db)
+    {
+        var settings = await db.SiteSettings
+            .AsNoTracking()
+            .Where(item => item.Id == 1)
+            .Select(item => new
+            {
+                item.HostImageData,
+                item.HostImageContentType,
+                item.HostImageUpdatedAt,
+            })
+            .FirstOrDefaultAsync();
+
+        if (settings?.HostImageData is not { Length: > 0 } imageData
+            || string.IsNullOrWhiteSpace(settings.HostImageContentType))
+        {
+            return Results.NotFound();
+        }
+
+        var entityTag = settings.HostImageUpdatedAt?.ToUnixTimeSeconds().ToString(System.Globalization.CultureInfo.InvariantCulture)
+            ?? imageData.Length.ToString(System.Globalization.CultureInfo.InvariantCulture);
+        return Results.File(
+            imageData,
+            settings.HostImageContentType,
+            entityTag: new Microsoft.Net.Http.Headers.EntityTagHeaderValue($"\"host-{entityTag}\""),
+            lastModified: settings.HostImageUpdatedAt);
+    }
+}