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/Migrations/AwardsDbContextModelSnapshot.cs

@@ -77,6 +77,51 @@ namespace Backend.Migrations
                     b.ToTable("AdminAuditEntries");
                 });
 
+            modelBuilder.Entity("Backend.Domain.ArchivedWinner", b =>
+                {
+                    b.Property<int>("Id")
+                        .ValueGeneratedOnAdd()
+                        .HasColumnType("integer");
+
+                    NpgsqlPropertyBuilderExtensions.UseIdentityByDefaultColumn(b.Property<int>("Id"));
+
+                    b.Property<string>("Category")
+                        .IsRequired()
+                        .HasMaxLength(120)
+                        .HasColumnType("character varying(120)");
+
+                    b.Property<DateTimeOffset>("CreatedAt")
+                        .HasColumnType("timestamp with time zone");
+
+                    b.Property<string>("Subcategory")
+                        .IsRequired()
+                        .HasMaxLength(120)
+                        .HasColumnType("character varying(120)");
+
+                    b.Property<DateTimeOffset?>("UpdatedAt")
+                        .HasColumnType("timestamp with time zone");
+
+                    b.Property<string>("WinnerName")
+                        .IsRequired()
+                        .HasMaxLength(120)
+                        .HasColumnType("character varying(120)");
+
+                    b.Property<string>("WinnerUrl")
+                        .IsRequired()
+                        .HasMaxLength(500)
+                        .HasColumnType("character varying(500)");
+
+                    b.Property<int>("Year")
+                        .HasColumnType("integer");
+
+                    b.HasKey("Id");
+
+                    b.HasIndex("Year", "Category", "Subcategory")
+                        .IsUnique();
+
+                    b.ToTable("ArchivedWinners");
+                });
+
             modelBuilder.Entity("Backend.Domain.AwardResult", b =>
                 {
                     b.Property<int>("Id")
@@ -779,11 +824,26 @@ namespace Backend.Migrations
                         .IsRequired()
                         .HasColumnType("text");
 
+                    b.Property<string>("HostArtistName")
+                        .IsRequired()
+                        .HasMaxLength(120)
+                        .HasColumnType("character varying(120)");
+
                     b.Property<string>("HostDisplayName")
                         .IsRequired()
                         .HasMaxLength(120)
                         .HasColumnType("character varying(120)");
 
+                    b.Property<string>("HostImageContentType")
+                        .HasMaxLength(80)
+                        .HasColumnType("character varying(80)");
+
+                    b.Property<byte[]>("HostImageData")
+                        .HasColumnType("bytea");
+
+                    b.Property<DateTimeOffset?>("HostImageUpdatedAt")
+                        .HasColumnType("timestamp with time zone");
+
                     b.Property<string>("HostTagline")
                         .IsRequired()
                         .HasMaxLength(160)