Implement LLM provider configuration and update user settings

- Added functionality to update the default LLM provider for users via a new endpoint in UserController.
- Introduced LlmProvider enum to manage available LLM options: Auto, Gemini, OpenAI, and Claude.
- Updated User and UserEntity models to include DefaultLlmProvider property.
- Enhanced database context and migrations to support the new LLM provider configuration.
- Integrated LLM services into the application bootstrap for dependency injection.
- Updated TypeScript API client to include methods for managing LLM providers and chat requests.

src/Managing.Infrastructure.Database/PostgreSql/ManagingDbContext.cs

@@ -105,6 +105,9 @@ public class ManagingDbContext : DbContext
                 .HasConversion<string>(); // Store enum as string
             entity.Property(e => e.DefaultExchange)
                 .HasConversion<string>(); // Store enum as string
+            entity.Property(e => e.DefaultLlmProvider)
+                .HasConversion<string>() // Store enum as string
+                .HasDefaultValueSql("'Auto'"); // Default LLM provider
             
             // Create indexes for performance
             entity.HasIndex(e => e.Name).IsUnique();