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/Data/AwardsDbContext.cs

@@ -10,6 +10,7 @@ public sealed class AwardsDbContext(DbContextOptions<AwardsDbContext> options) :
     public DbSet<Candidate> Candidates => Set<Candidate>();
     public DbSet<StreamerIdentity> StreamerIdentities => Set<StreamerIdentity>();
     public DbSet<AwardResult> Results => Set<AwardResult>();
+    public DbSet<ArchivedWinner> ArchivedWinners => Set<ArchivedWinner>();
     public DbSet<Nomination> Nominations => Set<Nomination>();
     public DbSet<VoteBallot> VoteBallots => Set<VoteBallot>();
     public DbSet<VoteEntry> VoteEntries => Set<VoteEntry>();
@@ -40,6 +41,9 @@ public sealed class AwardsDbContext(DbContextOptions<AwardsDbContext> options) :
         {
             entity.Property(item => item.HostDisplayName).HasMaxLength(120);
             entity.Property(item => item.HostTagline).HasMaxLength(160);
+            entity.Property(item => item.HostArtistName).HasMaxLength(120);
+            entity.Property(item => item.HostImageData).HasColumnType("bytea");
+            entity.Property(item => item.HostImageContentType).HasMaxLength(80);
             entity.Property(item => item.NewsletterUrl).HasMaxLength(400);
             entity.Property(item => item.PrivacyEmail).HasMaxLength(160);
             entity.Property(item => item.PrivacyPolicyUpdatedBy).HasMaxLength(120);
@@ -186,6 +190,15 @@ public sealed class AwardsDbContext(DbContextOptions<AwardsDbContext> options) :
             entity.Property(item => item.CategoryName).HasMaxLength(120);
         });
 
+        modelBuilder.Entity<ArchivedWinner>(entity =>
+        {
+            entity.HasIndex(item => new { item.Year, item.Category, item.Subcategory }).IsUnique();
+            entity.Property(item => item.Category).HasMaxLength(120);
+            entity.Property(item => item.Subcategory).HasMaxLength(120);
+            entity.Property(item => item.WinnerName).HasMaxLength(120);
+            entity.Property(item => item.WinnerUrl).HasMaxLength(500);
+        });
+
         modelBuilder.Entity<UserSession>(entity =>
         {
             entity.HasIndex(item => item.SessionToken).IsUnique();