Implement asynchronous bumper rendering and add integration tests: refactor BumperAsset to support async rendering, introduce BumperRenderBackgroundService for processing, and create TeleWave.Integration.Tests with Testcontainers-Postgres for comprehensive testing of scheduling and bumper generation scenarios. Update documentation and ensure tests skip if Docker is not available.

backend/src/TeleWave.Infrastructure/Migrations/AppDbContextModelSnapshot.cs

@@ -164,6 +164,9 @@ namespace TeleWave.Infrastructure.Migrations
                     b.Property<Guid>("Id")
                         .HasColumnType("uuid");
 
+                    b.Property<Guid>("ChannelId")
+                        .HasColumnType("uuid");
+
                     b.Property<DateTimeOffset>("CreatedAt")
                         .HasColumnType("timestamp with time zone");
 
@@ -178,9 +181,15 @@ namespace TeleWave.Infrastructure.Migrations
                         .HasMaxLength(128)
                         .HasColumnType("character varying(128)");
 
+                    b.Property<Guid>("TemplateId")
+                        .HasColumnType("uuid");
+
                     b.Property<Guid>("ToShowId")
                         .HasColumnType("uuid");
 
+                    b.Property<Guid>("VariantId")
+                        .HasColumnType("uuid");
+
                     b.HasKey("Id");
 
                     b.HasIndex("FromShowId", "ToShowId", "Signature");