Add SQL outbox for MAX sends

server/QMax.Api/Program.cs

@@ -95,7 +95,9 @@ builder.Services.AddScoped<ChatProjectionService>();
 builder.Services.AddScoped<IPushNotificationService, FirebasePushNotificationService>();
 builder.Services.AddSingleton<IAttachmentStorageService, AttachmentStorageService>();
 builder.Services.AddSingleton<MaxBridgeSyncService>();
+builder.Services.AddScoped<MaxOutboxService>();
 builder.Services.AddHostedService<MaxSyncWorker>();
+builder.Services.AddHostedService<MaxOutboxWorker>();
 
 if (string.Equals(configuredOptions.MaxMode, "Mock", StringComparison.OrdinalIgnoreCase))
 {
@@ -176,6 +178,11 @@ static async Task EnsureCompatibilitySchemaAsync(QMaxDbContext db)
         ON Messages (ChatId, ExternalId);
         """);
 
+    await db.Database.ExecuteSqlRawAsync("""
+        CREATE INDEX IF NOT EXISTS IX_Messages_DeliveryState_SentAt
+        ON Messages (DeliveryState, SentAt);
+        """);
+
     await db.Database.ExecuteSqlRawAsync("""
         CREATE TABLE IF NOT EXISTS MessageReactions (
             Id TEXT NOT NULL CONSTRAINT PK_MessageReactions PRIMARY KEY,